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Transcript of Data Modeling
1
Data Modeling and Database Design Volume One
Student Guide
ORACLE Enabling the Information Age ™
2
June 1992
M00475
ORACLE
Data Modeling and Database Design Student Guide • Volume One
3
Data Modelling and Database Design
Contributors: Ann Horton
Howard Benbrook
Dean Dameron
Art Hetherington
Jeff Jacobs
Steve Strickland
Kathy Andronica
Pete Cassidy
Claudia Herzog
Bill Hopkins
Cliff Longman
Tom Traver
Publishing: Scott Knudtson Rich Marinaccio
Copyright © Oracle Corporation, 1992
All rights reserved. Printed in the U.S.A.
This software/documentation contains proprietary information of Oracle Corporation; it is provided under a license
agreement containing restrictions on use and disclosure and is also protected by copyright law. Reverse engineering of the
software is prohibited. If this software/documentation is delivered to a U.S. Government Agency of the Department of
Defense, then it is delivered with Restricted Rights and the following legend is applicable:
Restricted Rights Legend
Use, duplication or disclosure by the Government is subject to restrictions for commercial computer software and shall be
deemed to be Restricted Rights software under Federal law and as set forth in subparagraph (c) (1) (ii) of DFARS 252.227-
7013, Rights in Technical Data and Computer Software (October 1988).
Use, duplication, or disclosure is subject to restrictions stated in your contract with Oracle Corporation.
If this software/documentation is delivered to a U.S. Government Agency not within the Department of Defense, then it is
delivered with "Restricted Rights." as defined in FAR 52.227-14, Rights in Data-General, including Alternate III (June
1987).
The information in this document is subject to change without notice. If you find any problems in the documentation, please
report them to us in writing to Oracle Corporation. 500 Oracle Parkway, Redwood Shores. CA 94065-9815. Oracle
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4
CONTENTS
CONTENTS .............................................................................................................................. 4
1 INTRODUCTION.....................................................................................9
COURSE OBJECTIVES ....................................................................................................... 10
ORACLE OVERVIEW......................................................................................................... 11
ORACLE'S CASE APPROACH .......................................................................................... 13
CASE*METHOD DEVELOPMENT CYCLE.................................................................... 14
2 OVERVIEW OF DATABASE DEVELOPMENT..................................15
SECTION OBJECTIVES...................................................................................................... 16
DATABASE DEVELOPMENT PROCESS ........................................................................ 17
BUSINESS INFORMATION REQUIREMENTS .............................................................. 18
CONCEPTUAL DATA MODELLING OVERVIEW ....................................................... 19
DATABASE DESIGN OVERVIEW.................................................................................... 20
DATABASE BUILD OVERVIEW....................................................................................... 21
DATABASE AND APPLICATION DEVELOPMENT..................................................... 22
3 BASIC CONCEPTUAL DATA MODELLING......................................23
SECTION OBJECTIVES...................................................................................................... 24
CONCEPTUAL DATA MODELLING ............................................................................... 25
ENTITIES ............................................................................................................................... 29
IDENTIFY AND MODEL ENTITIES................................................................................. 33
EXERCISE 3-1 ....................................................................................................................... 36
RELATIONSHIPS ................................................................................................................. 37
EXERCISE 3-2 ....................................................................................................................... 41
EXERCISE 3-3 ....................................................................................................................... 42
5
EXERCISE 3-4 ....................................................................................................................... 43
RELATIONSHIP TYPES ..................................................................................................... 44
USING A RELATIONSHIP MATRIX................................................................................ 48
ANALYZE AND MODEL RELATIONSHIPS................................................................... 50
DETERMINE A RELATIONSHIP'S EXISTENCE.......................................................... 51
NAME THE RELATIONSHIP............................................................................................. 53
DETERMINE RELATIONSHIP'S OPTIONALITY......................................................... 55
DETERMINE RELATIONSHIP'S DEGREE .................................................................... 56
VALIDATE THE RELATIONSHIP.................................................................................... 57
EXERCISE 3-5 ....................................................................................................................... 58
EXERCISE 3-6 ....................................................................................................................... 60
LAY OUT THE E-R DIAGRAM ......................................................................................... 62
ATTRIBUTES ........................................................................................................................ 64
DISTINGUISH ATTRIBUTES AND ENTITIES ............................................................... 69
ATTRIBUTE OPTIONALITY............................................................................................. 71
IDENTIFY ATTRIBUTES.................................................................................................... 73
EXERCISE 3-7 ....................................................................................................................... 75
ASSIGN UNIQUE IDENTIFIERS....................................................................................... 77
EXERCISE 3-8 ....................................................................................................................... 83
EXERCISE 3-9 ....................................................................................................................... 84
EXERCISE 3-10 ..................................................................................................................... 86
REVIEW: BASIC CONCEPTUAL DATA MODELLING............................................... 88
4 ADVANCED CONCEPTUAL DATA MODELLING............................92
SECTION OBJECTIVES...................................................................................................... 93
NORMALIZE THE DATA MODEL................................................................................... 94
EXERCISE 4-1 ....................................................................................................................... 98
6
RESOLVE M:M RELATIONSHIPS ................................................................................... 99
EXERCISE 4-2 ..................................................................................................................... 107
EXERCISE 4-3 ..................................................................................................................... 108
MODEL HIERARCHICAL DATA ................................................................................... 109
MODEL RECURSIVE RELATIONSHIPS ...................................................................... 112
EXERCISE 4-4 ..................................................................................................................... 117
MODEL ROLES WITH RELATIONSHIPS .................................................................... 118
MODEL SUBTYPES ........................................................................................................... 120
MODEL EXCLUSIVE RELATIONSHIPS ...................................................................... 124
EXERCISE 4-5 ..................................................................................................................... 126
MODEL DATA OVER TIME............................................................................................ 128
EXERCISE 4-6 ..................................................................................................................... 132
MODEL COMPLEX RELATIONSHIPS ......................................................................... 133
EXERCISE 4-7 ..................................................................................................................... 135
EXERCISE 4-8 ..................................................................................................................... 136
EXERCISE 4-9 ..................................................................................................................... 138
5 RELATIONAL DATABASE CONCEPTS...........................................139
SECTION OBJECTIVES.................................................................................................... 140
RELATIONAL DATABASE OVERVIEW ...................................................................... 141
PRIMARY KEYS................................................................................................................. 143
FOREIGN KEYS ................................................................................................................. 147
DATA INTEGRITY............................................................................................................. 149
6 INITIAL DATABASE DESIGN ...........................................................151
SECTION OBJECTIVES.................................................................................................... 152
DATABASE DESIGN.......................................................................................................... 153
INITIAL DATABASE DESIGN OVERVIEW ................................................................. 155
7
MAP SIMPLE ENTITIES................................................................................................... 158
MAP ATTRIBUTES TO COLUMNS................................................................................ 159
MAP UID'S TO PRIMARY KEYS .................................................................................... 161
MAP RELATIONSHIPS TO FOREIGN KEYS .............................................................. 163
REVIEW: MAPPING SIMPLE E-R MODELS TO TABLES........................................ 169
EXERCISE 6-1 ..................................................................................................................... 170
EXERCISE 6-2 ..................................................................................................................... 172
EXERCISE 6-3 ..................................................................................................................... 174
EXERCISE 6-4 ..................................................................................................................... 176
MAP COMPLEX E-R MODELS TO TABLES ............................................................... 179
EXERCISE 6-5 ..................................................................................................................... 183
CHOOSE SUBTYPE OPTIONS ........................................................................................ 187
EXERCISE 6-6 ..................................................................................................................... 196
REVIEW: INITIAL DATABASE DESIGN ...................................................................... 200
7 TABLE NORMALIZATION................................................................201
SECTION OBJECTIVES.................................................................................................... 202
NORMALIZE TABLES ...................................................................................................... 203
RECOGNIZE UNNORMALIZED DATA ........................................................................ 204
CONVERT TO FIRST NORMAL FORM........................................................................ 205
CONVERT TO SECOND NORMAL FORM................................................................... 206
CONVERT TO THIRD NORMAL FORM....................................................................... 208
EXERCISE 7-1 ..................................................................................................................... 210
NORMALIZE DURING DATA MODELLING............................................................... 214
8 FURTHER DATABASE DESIGN........................................................217
SECTION OBJECTIVES.................................................................................................... 218
FURTHER DATABASE DESIGN ..................................................................................... 219
8
SPECIFY REFERENTIAL INTEGRITY......................................................................... 220
DESIGN INDEXES.............................................................................................................. 222
ESTABLISH VIEWS ........................................................................................................... 227
DENORMALIZE THE DATABASE DESIGN................................................................. 230
PLAN PHYSICAL STORAGE USAGE............................................................................ 237
SUMMARY: DATABASE DESIGN .................................................................................. 238
SUMMARY: DATABASE DEVELOPMENT.................................................................. 239
DATABASE BUILD OVERVIEW..................................................................................... 240
9
1
INTRODUCTION
10
COURSE OBJECTIVES
At the end of this course, you will be able to:
1 Analyze user information requirements and develop an entity-relationship model to express
those requirements.
2 Develop a rela tional database design from an entity-relationship model.
11
ORACLE OVERVIEW
12
ORACLE Overview - cont'd
* Data Modelling and Database Design are techniques for analyzing
information requirements and designing relational databases.
13
ORACLE'S CASE APPROACH
Oracle's CASE (Computer-Aided Systems Engineering) approach provides
a full-suite of CASE methods, techniques and tools.
Business Requirements
Operational System
14
CASE*METHOD DEVELOPMENT CYCLE
Data modeling and database design support the first three stages of the
CASE*Method Development cycle.
15
2
OVERVIEW OF
DATABASE DEVELOPMENT
16
SECTION OBJECTIVES
At the end of this section, you will be able to:
1 Understand the phases of the Database Development Process.
2 Explain what Conceptual Data Modelling and Database Design involve.
3 Understand the parallel phases of the Application Development Process.
17
DATABASE DEVELOPMENT PROCESS
Database development is a top-down, systematic approach that transforms
business information requirements into an operational database.
The Database Development Process is a vertical slice of the CASE*Method
Development Cycle.
18
BUSINESS INFORMATION REQUIREMENTS
Top-down database development begins with the information requirements
of the business.
Example
Here is a set of information requirements:
"I manage the Human Resources Department for a large company. We need to keep information
about each of our company's employees. We need to track each employee's first name, last
name, job or position, hire date, and salary. For any employees on commission, we also need to
track their potential commission. Each employee is assigned a unique employee number.
Our company is divided into departments. Each employee is assigned to a department-for
example, accounting, sales, or development. We need to know the department responsible for
each employee and the department's location. Each department has a unique number, for
example, accounting is 10 and sales are 30.
Some of the employees are managers. We need to know each employee's manager, and the
employees each manager manages."
Quick Notes
• The scope of a set of information requirements may vary from the needs of a department to
the needs of a total company.
• Information requirements are tightly coupled with business function requirements. For
example, the Human Resources Department's business function requirements include Manage
employee information.
19
CONCEPTUAL DATA MODELLING OVERVIEW
In Conceptual Data Modelling, define and model the things of significance
about which the business needs to know or hold information, and the
relationships between them.
Example
The following entity-relationship model represents the information requirements of the Human
Resources Department.
An Entity-Relationship Data Model should accurately model the
organization's information needs and support the functions of the business.
20
DATABASE DESIGN OVERVIEW
In Database Design, map the information requirements reflected in an
Entity-Relationship Model into a relational database design.
Example
A design for the Human Resources database is shown in the following table instance charts.
Table Name: EMPLOYEE
Column Name
EMPN
O
FNAM
E
LNAME
JOB
HIREDATE
SA
L
COM
M
MGR
DEPTN
O Key Type PK FK1 FK2
Nulls/ Unique NN, U NN NN NN NN
7369 MARY SMITH CLERK 17-DEC-80 80 7902 20
7902 HENR FORD ANALYST 03-DEC-81 30 7566 50
7521
SUE
WARD
SALESMA
N
22-FEB-81
12
51
6000
7698
30
7698
BOB
BLAKE
MANAGER
01-MAY-81
28
50
1000
0
7839
30
Sample Data
7839 BOB KING PRESIDEN 17-NOV-81 50 5000 10
Table Name: DEPARTMENT
Column Name
DEPTNO
DNAME
LOC
Key Type
PK
Nulls/ Unique NN, U NN NN
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
Sample Data
50 DEVELOPMENT ATLANTA
The Table Instance Chart for each relational table identifies the table's
columns, primary key, and any foreign keys and provides a visual view of
sample data.
21
DATABASE BUILD OVERVIEW
In Database Build, create physical relational database tables to implement
the database design.
Example
The following Structured Query Language (SQL) statements will create the DEPARTMENT and
EMPLOYEE tables.
SQL> CREATE TABLE DEPARTMENT 2 (DEPTNO NUMBER(2) NOT NULL PRIMARY KEY, 3 DNAME CHAR(20) NOT NULL, 4 LOC CHAR 115) NOT NULL );
SQL> CREATE TABLE EMPLOYEE 2 (EMPNO NUMBER (5) NOT NULL PRIMARY KEY, 3 FNAME CHAR(15) NOT NULL, 4 LNAME CHAR(15) NOT NULL, 5 JOB CHAR(9), 6 HIREDATE DATE NOT NULL, 7 SAL NUMBER (7,2), 8 COMM NUMBER (7, 2), 9 MGR CHAR(4) REFERENCES EMPLOYEE(EMPNO),
10 DEPTNO NUMBER(2) NOT NULL REFERENCES DEPARTMENT (DEPTNO) );
The Structured Query Language (SQL) is used to create and manipulate
relational databases.
22
DATABASE AND APPLICATION DEVELOPMENT
The Database Development Process is tightly coupled with the Application
Development Process.
23
3
BASIC
CONCEPTUAL DATA MODELLING
24
SECTION OBJECTIVES
At the end of this section, you will be able to:
1. Identify and model entities.
2. Analyze and model the relationships between entities.
3. Analyze and model attributes.
4. Identify unique identifiers for each entity.
5. Develop a basic entity-relationship model from a statement of information requirements and
user interviews.
25
CONCEPTUAL DATA MODELLING
Conceptual Data Modelling is the first step of the top-down Database
Development Process, and is performed during the Strategy and Analysis
stages of the System Development Cycle.
26
Conceptual Data Modelling-cont'd
The goal of Conceptual Data Modeling is to develop an entity-relationship
model that represents the information requirements of the business.
Example
The following entity-relationship model represents the information requirements of the Human
Resources Department.
Entity-Relationship Model Components
• Entities - the things of significance about which information needs to be held.
• Relationships-how the things of significance are related.
• Attributes-the specific information, which needs to be held.
27
Conceptual Data Modelling-cont'd
An entity-relationship model is an effective means for collecting and
documenting an organization's information requirements.
Robust Syntax
• An E-R Model documents an organization's information requirements in a clear, precise
format.
User Communication
• Users can easily understand the pictorial form of an E-R Model.
Ease of Development
• An E-R Model can be easily developed and refined.
Definition of Scope
• An E-R Model provides a clear picture of the scope of an organization's information
requirements.
Integration of Multiple Applications
• An E-R Model provides an effective framework for integrating multiple applications,
development projects, and/or purchased application packages.
Quick Notes
• Be sure to fully establish an organization's information requirements during the conceptual
data modelling stage. Requirements changes during later stages of the development life-cycle
can be extremely expensive.
• Use views or subsets of an E-R Model as a communication aide.
28
Conceptual Data Modelling-cont'd
Conceptual Data Modelling is independent of the hardware or software to
be used for implementation. An E-R Model can be mapped to a
hierarchical, network, or relational database.
29
ENTITIES
An entity is a thing of significance about which information needs to be
known or held.
Alternate Entity Definitions
• An object of interest to the business.
• An entity is a class or category of thing.
• An entity is a named thing.
Examples
The following might be things of significance about which a business needs to hold information:
EMPLOYEE
DEPARTMENT
PROJECT
Attributes describe entities and are the specific pieces of information, which
need to be known.
Examples
Possible attributes for the entity EMPLOYEE are:
badge number, name, date of birth, and salary
Possible attributes for the entity DEPARTMENT are:
Name, number, and location
Quick Note
• An entity must have attributes that need to be known from the business's viewpoint or it is not
an entity within the scope of the business's requirements.
30
Entities - cont'd
Entity Diagramming Conventions
• Soft box with any dimensions
• Singular, unique entity name
• Entity name in upper case
• Optional synonym name (in parentheses)
• Attribute names in all lower case
Examples
Quick Notes
• A synonym is an alternate name for an entity.
• Synonyms are useful when two groups of users have different names for the same thing of
significance.
31
Entities - cont'd
Each entity must have multiple occurrences or instances.
Examples
The entity EMPLOYEE has one occurrence for each employee in the business:
Jim Brown, Mary Jones, Juan Gomez, and Jill Judge are all occurrences of the entity
EMPLOYEE.
The entity DEPARTMENT has one occurrence for each department in the company:
The Finance Department, the Sales Department, and the Development Department are all
instances of the entity DEPARTMENT.
Each entity instance has specific values for the entity's attributes.
Example
The entity EMPLOYEE has attributes of name, badge number, date of birth, and salary.
The instance Jim Brown has the following values: name Jim Brown, badge number 1322, date
of birth 15-MAR-50, and salary $55,000.
Quick Notes
• Instances are sometimes mistaken for entities.
• An entity is a class or category of thing - e.g. EMPLOYEE.
• An instance is a specific thing - e.g. the employee Jim Brown.
32
Entities - cont'd
Each instance must be uniquely identifiable from other instances of the same entity. An attribute or set
of attributes that uniquely identify an entity is called a Unique Identifier (UID).
Example
Each employee has a unique badge number. Badge number is a candidate for the entity EMPLOYEE'S
UID.
Look for attributes that uniquely identify an entity.
Example
What attributes might uniquely identify the following entities?
Quick Notes
• If an entity cannot be uniquely identified, it may not be an entity.
• Attributes, which uniquely identify an entity and are part of
the entity's UID are tagged with #*.
33
IDENTIFY AND MODEL ENTITIES
Follow the steps below to identify and model entities from a set of interview
notes.
• Examine the nouns. Are they things of significance?
• Name each entity.
• Is there information of interest about the entitiy that the-business needs to hold?
• Is each instance of the entity uniquely identifiable? Which attribute or attributes could serve as
its UID?
• Write a description of it. "An EMPLOYEE has significance as a paid worker at the company.
For example, John Brown and Mary Smith are EMPLOYEES."
• Diagram each entity and a few of its attributes.
Quick Note
• Do not disqualify a candidate entity too soon. Additional attributes of interest to the business
may be uncovered later.
34
Identify and Model Entities - cont'd
Example
Identify and model the entities in the following set of information requirements.
"I'm the manager of a training company that provides instructor-led courses in management
techniques. We teach many courses, each of which has a code, a name, and a fee. Introduction
to UNIX and C Programming-are two of our more popular courses. Courses vary in length from
one day to four days. An instructor can teach several courses. Paul Rogers and Maria Gonzales
are two of our best teachers. We track each instructor's name and phone number. Each course is
taught by only one instructor. We create a course and then line up an instructor. The students
can take several courses over time, and many of them do this. Jamie Brown from AT&T took
every course we offer! We track each student's name and phone number. Some of our students
and instructors do not give us their phone numbers.
35
Identify and Model Entities - cont'd
Solution
The following entities model the Training Company's information requirements.
Entity Descriptions
• A COURSE has significance as a training event offered by the Training Company. For
example, Introduction to UNIX and C Programming.
• A STUDENT has significance as a participant in one or more COURSES. For example, Jamie
Brown.
• An INSTRUCTOR has significance as a teacher of one or more COURSES. For example, Paul
Rogers and Maria Gonzales.
36
EXERCISE 3-1
Identify and model entities.
1. Identify and model the entities in the following set of information requirements. Write a brief
description of each entity. Show at least two attributes for each entity.
"I'm the owner of a small video store. We have over 3,000 videotapes that we need to keep track
of.
Each of our videotapes has a tape number. For each movie, we need to know its title and
category (e.g. comedy, suspense, drama, action, war, or sci-fi). Yes, we do have multiple copies
of many of our movies. We give each movie a specific id, and then track which movie a tape
contains. A tape may be either Beta or VHS format. We always have at least one tape for each
movie we track, and each tape is always a copy of a single, specific movie. Our tapes are very
long and we don't have any movies, which require multiple tapes.
We are frequently asked for movies starring specific actors. John Wayne and Katherine
Hepburn are always popular. So we'd like to keep track of the star actors appearing in each
movie. Not all of our movies have star actors. Customers like to know each actor's "real" birth
name and date of birth. We track only actors who appear in the movies in our inventory.
We have lots of customers. We only rent videos to people who have joined our "video club." To
belong to our club, they must have good credit. For each club member, we’d like to keep his/her
first and last name, current phone number, and current address. And, of course each club
member has a membership number.
Then we need to keep track of what videotapes each customer currently has checked out. A
customer may check out multiple videotapes at any given time. We just track current rentals.
We don't keep track of any rental histories."
37
RELATIONSHIPS
A relationship is a two-directional, significant association between two
entities, or between an entity and itself.
Relationship Syntax
Example
The relationship between INSTRUCTOR and COURSE is:
Each COURSE may be taught by one and only one INSTRUCTOR.
Each INSTRUCTOR may be assigned to one or more courses.
Each direction of a relationship has:
• a name - e.g., taught by or assigned to.
• an optionality - either must be or may be.
• a degree - either one and only one or one or more.
Quick Notes
• Cardinality is a synonym for the term degree.
• A degree of 0 is addressed by may be.
38
Relationships - cont'd
Diagramming Conventions
• A line between two entities
• Lower case relationship names
• Optionality
• Degree
39
Relationships - cont'd
First read a relationship in one direction, and then read the relationship in
the other direction.
Example
Read the relationship between EMPLOYEE and DEPARTMENT.
Read this relationship first from left to right, and then from right to left.
Relationship from Left to Right (partial diagram)
Each EMPLOYEE must be assigned to one and only one DEPARTMENT.
Relationship from Right to Left (partial diagram)
Each DEPARTMENT may be responsible for one or more EMPLOYEES.
40
Relationships - cont'd
Example
Read the relationship between STUDENT and COURSE.
Each STUDENT may be enrolled in one or more COURSES.
Each COURSE may be taken by one or more STUDENTS.
Example
Read the relationship between PAYCHECK and EMPLOYEE.
Each PAYCHECK must be for one and only one EMPLOYEE.
Each EMPLOYEE may be the receiver of one or more PAYCHECKs.
41
EXERCISE 3-2
Read relationships.
1. Write the relationship sentences for this E-R diagram.
42
EXERCISE 3-3
Draw an Entity-Relationship Diagram.
1. Draw an Entity-Relationship diagram to represent the following:
a. Each EMPLOYEE must be assigned to one and only one DEPARTMENT.
b. Each DEPARTMENT may be responsible for one or more EMPLOYEES.
c. Each EMPLOYEE may be assigned to one or more ACTIVITIES.
d. Each ACTIVITY may be performed by one or more EMPLOYEES.
43
EXERCISE 3-4
Optional Exercise
Draw an Entity-Relationship Diagram.
1. Draw an Entity-Relationship diagram to represent the following:
a. Each ORACLE DATABASE must be made up of one or more TABLESPACEs.
b. Each TABLESPACE must be part of one and only one ORACLE DATABASE.
c. Each TABLESPACE must be made up of one or more FILEs.
d. Each FILE may be part of one and only one TABLESPACE.
e. Each TABLESPACE may be divided into one or more SEGMENTS.
f. Each SEGMENT must be included in one and only one TABLESPACE.
g. Each SEGMENT must be inclusive of one or more EXTENTS.
h. Each EXTENT must be included in one and only one SEGMENT.
i. Each EXTENT must be composed of one or more BLOCKs.
j. Each BLOCK must be part of one and only one EXTENT.
k. Each FILE must be resident on one and only one DISK. *
l. Each DISK may be the host for one or more FILEs.
* Some operating systems may allow a file to span disks.
44
RELATIONSHIP TYPES
There are three types of relationships.
Relationship Types
• Many to One Relationships
• Many to Many Relationships
• One to One Relationships
All relationships should represent the information requirements and rules of the business.
45
Relationship Types - cont'd
A Many to One Relationship (M to 1 or M:1) has a degree of one or more in
one direction and a degree of one and only one in the other direction.
Example
There is a M:1 relationship between CUSTOMER and SALES REPRESENTATIVE.
Each CUSTOMER must be visited by one and only one SALES REPRESENTATIVE.
Each SALES REPRESENTATIVE may be assigned to visit one or more CUSTOMERS.
Quick Notes
• M:1 relationships are very common.
• M:1 relationships that are mandatory in both directions are rare.
46
Relationship Types - cont'd
A Many to Many Relationship (M to M or M:M) has a degree of one or
more in both directions.
Examples
There is a M:M relationship between STUDENT and COURSE.
Each STUDENT may be enrolled in one or more COURSES.
Each COURSE may be taken by one or more STUDENTS.
There is a M:M relationship between EMPLOYEE and JOB.
Each EMPLOYEE may be assigned to one or more JOBs.
Each JOB may be carried out by one or more EMPLOYEES.
Quick Notes
• Many to Many Relationships are very common.
• Many to Many relationships are usually optional in both directions, although a Many to Many
Relationship may be optional in just one direction.
47
Relationship Types - cont'd
A One to One Relationship (1 to 1 or 1:1) has a degree of one and only one
in both directions.
Example
There is a 1:1 relationship between MICROCOMPUTER and MOTHERBOARD.
Each MICROCOMPUTER must be the host for one and only one MOTHERBOARD.
Each MOTHERBOARD may be incorporated into one and only one MICROCOMPUTER.
Quick Notes
• 1:1 Relationships are rare.
• A 1:1 Relationship that is mandatory in both directions is very rare.
• Entities, which seem to have a 1:1 relationship, may really be the same entity.
48
USING A RELATIONSHIP MATRIX
Use a relationship matrix as an aide for the initial collection of information
about the relationships between a set of entities.
Relationship Matrix Conventions
• A relationship matrix shows if and how each row entity on the left-hand side of the matrix is
related to each column entity shown across the top of the matrix.
• All the entities are listed along both the left-hand side of the matrix and the top of the matrix.
• If a row entity is related to a column entity, then the name of that relationship is shown in the
intersection box.
• If a row entity is not related to a column entity, then a long dash is shown in the intersection
box.
• Each relationship above the diagonal line is the inverse or mirror image of a relationship
below the line.
• Recursive relationships (between an entity and itself) are represented by the boxes on the
diagonal.
Example
The following relationship matrix shows a set of relationships between four entities.
CUSTOMER is related to ORDER and the name of the relationship is the originator of. ORDER is related to CUSTOMER and the name of the relationship is originated by.
49
Using a Relationship Matrix - cont'd
Map the contents of a relationship matrix to an E-R diagram.
Example
Map the following relationship matrix to an E-R diagram.
Draw a softbox for each entity and add the entity's attributes. Draw a relationship line for each
relationship, write-in the relationship's name, and add each relationship's optionality and degree.
50
ANALYZE AND MODEL RELATIONSHIPS
Follow a series of five steps to analyze and model relationships.
Steps
• Determine the existence of a relationship.
• Name each direction of the relationship.
• Determine the optionality of each direction of the relationship.
• Determine the degree of each direction of the relationship.
• Read the relationship aloud to validate it.
51
DETERMINE A RELATIONSHIP'S EXISTENCE
Determine the existence of a relationship.
Examine each pair of entities to determine if a
relationship exists.
Ask About a Relationship's Existence
• Does a significant relationship exist between ENTITY A and
ENTITY B?
Example
Consider the entities DEPARTMENT and EMPLOYEE.
Is there a significant relationship between DEPARTMENT and EMPLOYEE?
Yes, there is a significant relationship between DEPARTMENT and EMPLOYEE.
Example
Consider the entities DEPARTMENT and ACTIVITY.
Is there a significant relationship between DEPARTMENT and ACTIVITY?
No, there is not a significant relationship between DEPARTMENT and ACTIVITY.
52
Determine a Relationship's Existence - cont'd
Use a relationship matrix to systematically examine
each pair of entities.
Example
Log the relationships among ACTIVITY, DEPARTMENT, and EM-
PLOYEE on a relationship matrix. The check marks indicate that a
relationship exists.
53
NAME THE RELATIONSHIP
Name each direction of a relationship.
Ask a Relationship's Name
• How is an ENTITY A related to an ENTITY B?
An ENTITY A is relationship name an ENTITY B.
• How is an ENTITY B related to an ENTITY A?
An ENTITY B is relationship name an ENTITY A.
Example
Consider the relationship between DEPARTMENT and EMPLOYEE.
How is a DEPARTMENT related to an EMPLOYEE?
Each DEPARTMENT is responsible for an EMPLOYEE.
How is an EMPLOYEE related to a DEPARTMENT?
Each EMPLOYEE is assigned to a DEPARTMENT.
Optionally, log the relationship names in a relationship grid.
Example
Log the relationship names for the relationship between DEPARTMENT and EMPLOYEE.
54
Name the Relationship - cont'd
Use a list of relationship name pairs to assist in
naming relationships.
Useful Relationship Name Pairs
• based on the basis for
• bought from the supplier of
• description of for
• operated by the operator for
• represented by the representation of
• responsible for the responsibility of
Quick Note
• Do not use related to or associated with as relationship names.
For further information on the subject see:
CASE*Method Entity Relationship Modelling, 5456-V1.0, page C-10
55
DETERMINE RELATIONSHIP'S OPTIONALITY
Determine the optionality of each direction of the
relationship.
Ask About a Relationship's Optionality
• Must ENTITY A be relationship name ENTITY B?
• Must ENTITY B be relationship name ENTITY A?
Example
Consider the relationship between DEPARTMENT and EMPLOYEE.
Must an EMPLOYEE be assigned to a DEPARTMENT? Always?
Is there any situation in which an EMPLOYEE will not be assigned to a DEPARTMENT?
No, an EMPLOYEE must always be assigned to a DEPARTMENT.
Must a DEPARTMENT be responsible for an EMPLOYEE?
No, a DEPARTMENT does not have to be responsible for an EMPLOYEE.
Draw the relationship lines, with the relationship names.
Example
56
DETERMINE RELATIONSHIP'S DEGREE
Determine the degree of the relationship in both
directions.
Ask About a Relationship's Degree
• May ENTITY A be relationship name more than one ENTITY
B?
• May ENTITY B be relationship name more than one ENTITY
A?
Example
Consider the relationship between DEPARTMENT and EMPLOYEE.
May an EMPLOYEE be assigned to more than one DEPARTMENT?
No, an EMPLOYEE must be assigned to only one DEPARTMENT.
May a DEPARTMENT be responsible for more than one EMPLOYEE?
Yes, a DEPARTMENT may be responsible for one or more EMPLOYEES.
Add the relationship degrees to the E-R Diagram.
Example
57
VALIDATE THE RELATIONSHIP
Re-examine the E-R Model and validate the
relationship.
Read the Relationship Aloud
• Relationships must be readable and make business sense.
Example
Read the relationship represented by the following diagram.
Each EMPLOYEE must be assigned to one and only one DEPARTMENT.
Each DEPARTMENT may be responsible for one or more EMPLOYEES.
58
EXERCISE 3-5
Analyze and model relationships.
1. Analyze and model the relationships in the following set of information requirements. Use a
relationship matrix to track the existence of relationships between the entities.
"I'm the manager of a training company that provides instructor-led courses in management
techniques. We teach many courses, each of which has a code, a name, and a fee. Introduction
to UNIX and C Programming are two of our more popular courses. Courses vary in length from
one day to four days. An instructor can teach several courses. Paul Rogers and Maria Gonzales
are two of our best teachers. We track each instructor's name and phone number. Each course is
taught by only one instructor. We create a course and then line up an instructor. The students
can take several courses over time, and many of them do this. Jamie Brown from AT&T took
every course we offer! We track each student's name and phone number. Some of our students
and instructors do not give us their phone numbers."
59
Exercise 3-5 - cont'd
The following entities were previously modelled.
60
EXERCISE 3-6
Analyze and model relationships.
1. Analyze and model the relationships in the following set of information requirements from
Exercise 3-1. Use a relationship matrix to track the existence of relationships between the
entities.
"I'm the owner of a small video store. We have over 3,000 videotapes that we need to keep track
of.
Each of our videotapes has a tape number. For each movie, we need to know its title and
category (e.g. comedy, suspense, drama, action, war, or sci-fi). Yes, we do have multiple copies
of many of our movies. We give each movie a specific id, and then track which movie a tape
contains. A tape may be either Beta or VHS format. We always have at least one tape for each
movie we track, and each tape is always a copy of a single, specific movie. Our tapes are very
long, and we don't have any movies, which require multiple tapes.
We are frequently asked for movies starring specific actors. John Wayne and Katherine
Hepburn are always popular. So we'd like to keep track of the star actors appearing in each
movie. Not all of our movies have star actors. Customers like to know each actor's "real" birth
name and date of birth. We track only actors who appear in the movies in our inventory.
We have lots of customers. We only rent videos to people who have joined our "video club." To
belong to our club, they must have good credit. For each club member, we'd like to keep their
first and last name, current phone number, and current address. And, of course each club
member has a membership number.
Then we need to keep track of what videotapes each customer currently has checked out. A
customer may check out multiple videotapes at any given time. We just track current rentals.
We don't keep track of any rental histories."
61
Exercise 3-6 - cont'd
The following entities were modelled earlier in Exercise 3-1.
62
LAY OUT THE E-R DIAGRAM
Make an E-R Diagram easy to read and applicable to the people who need
to work with it.
Neat and Tidy
• Line entity boxes up.
• Draw relationship lines straight and either horizontal or vertical.
• Use an angle of 30° to 60°, which is easier to follow when relationship lines must cross.
• Use plenty of white space to avoid the look of congestion.
• Avoid the use of many closely parallel lines, which are difficult to follow.
Unambiguous Text
• Make all text unambiguous.
• Avoid abbreviations and jargon.
• Add adjectives to improve understanding.
• Align text horizontally.
• Put relationship names at the ends of the line and on opposite sides of the line.
Memorable Shapes
• Make the E-R Diagram memorable. People remember shapes and patterns.
• Do not draw an E-R Diagram on a grid.
• Stretch or shrink entity boxes to help the layout of the diagram.
63
Lay Out the E-R Diagram - cont'd
Draw crowsfeet pointing up or to the left.
Layout Rules
• Try to position a crowsfoot on the left end or the top end of the relationships line.
• Position higher volume, more volatile entities toward the top and left of the diagram.
• Position lower volume, less volatile entities toward the bottom and right of the diagram.
Quick Note
• Until an M:M relationship is resolved, at least one end of the relationship will point down or
to (he right.
For further information on the subject see:
CASE*Method Entity Relationship Modelling, 5456-V1.0, pp. 3-16 and 3-17.
64
ATTRIBUTES
Attributes are information about an entity that needs to be known or held.
Attributes describe an entity by qualifying, identifying, classifying,
quantifying or expressing the state of the entity.
Example
What are some attributes of the entity EMPLOYEE?
• Badge number or payroll number identify an EMPLOYEE.
• First name and last name qualify an EMPLOYEE.
• Payroll category (e.g. weekly or salary) classifies an EMPLOYEE.
• Age quantifies an EMPLOYEE.
• Employment status (e.g. active, on leave, terminated) expresses the status of an EMPLOYEE.
Attributes represent a type of description or detail, not an instance.
Example
77506 and 763111 are values of the attribute badge number.
John is a value of the attribute first name of EMPLOYEE.
Quick Notes
• Attribute names should be clear to the user, not codified for the developer.
• The entity's name is always a qualifier of the attribute name - e.g., code of COURSE.
Therefore, an attribute's name should not include its entity's name.
• Attribute names should be specific - e.g., is it quantity, quantity returned, or quantity
purchased?
• Always clarify a date attribute with a descriptor or verb phrase, e.g. date of contact, date
ordered.
• An attribute should only be assigned to a single entity.
65
Attributes - cont'd
Diagramming Conventions
• Attribute names are singular and shown in lower case.
• List attribute names in their entity's soft box.
Example
66
Attributes - cont'd
Always break attributes down into their lowest meaningful components.
Examples
The name of a PERSON can be broken down into last name and first name.
The number of an ITEM consists of type, vendor, and item number.
Break down aggregate attributes and embedded code fields into simple
attributes.
Quick Notes
• Attributes containing dates, times, social security numbers, and zip codes are generally not
decomposed further.
• An attribute of address is frequently left as an aggregate and then decomposed during Design.
Alternative ly it can be decomposed into multiple attributes: apartment/suite, street address,
city, state, and zip code.
• The level of attribute decomposition will depend upon the business requirements.
67
Attributes - cont'd
Verify that each attribute has a single value for each entity instance. A
multi-valued attribute or repeating group is not a valid attribute.
Example
Are the attributes of CLIENT single -valued?
No, a CLIENT may be contacted multiple times, and the business needs to keep all dates of contact. The entity CONTACT is missing.
Quick Note
• A repeated attribute indicates a missing entity.
68
Attributes - cont'd
Verify that an attribute is not derived or calculated from the existing values
of other attributes.
Common Derived Data
• Counts (e.g. the number of salesman in a region)
• Totals (e.g. the total number of each salesman's monthly sales)
• Max/Min/Average (e.g. statistics on the sales of a group of salesmen)
• Other calculations (e.g. a salesman's commission calculated at 10% of sales)
Do not include derived attributes in an E-R Model.
Quick Notes
• Derived attributes are redundant.
• Redundant data can lead to inconsistent data values. The derived data must be revised
whenever the attributes upon which it is based are revised.
• Address the option of storing derived data during Database Design.
69
DISTINGUISH ATTRIBUTES AND ENTITIES
If an attribute has attributes of its own, then it is really an entity.
Example
Determine if all of the attributes of VEHICLE are really attributes.
Initially the user identified color scheme as an attribute of VEHICLE. Later, the user defined the requirement to track the paint color, paint type, and trim color for each color scheme. Color scheme then had attributes of its own, and became an entity with a relationship to VEHICLE.
Example
Determine if all the attributes of EMPLOYEE are attributes.
Number of dependents is an attribute of EMPLOYEE, but if it is necessary to keep each dependent's name and age, then DEPENDENT becomes an entity. Number of dependents can now be derived.
Quick Notes
• Entities have attributes.
• Attributes have no attributes on their own.
70
Distinguish Attributes and Entities - cont'd
All entities are nouns, but not all nouns are entities.
Entity Characteristics Attribute Characteristics
Anything about which information must
be held
Qualifies an entity
Possesses one or more attributes
Does not possess attribute (s) of its own
If an entity has no attributes, it may be
only an attribute
If an attribute has an attribute, then it is an entity or
have no significance
May have multiple occurrences associated
with another entity via a relationship
Has a single value for each entity occurrence (no
repeating groups)
Quick Notes
• Do not disqualify a candidate entity too quickly. Attributes for that entity may appear later.
• Instances of entities and attributes are also nouns.
71
ATTRIBUTE OPTIONALITY
Identify each attribute's optionality using an attribute tag.
Mandatory Attributes
• A value must be known for each entity occurrence.
• Tagged with *.
Optional Attributes
• A value may be known for each entity occurrence.
• Tagged with o.
Example
Identify the attributes for the PERSON entity. Determine their optionality.
The title and weight attributes are optional. The remaining attributes are mandatory.
72
Attribute Optionality - cont'd
Use sample attribute instance data to validate attribute Optionality.
Example
Are the mandatory and optional attribute tags for the PERSON entity correct? Use an Entity Instance
Chart to validate that the mandatory and optional attribute tags for the PERSON entity are correct.
Entity Name: PERSON
Attribute Name code name title sex weight
Tags * * o * o
110 Jones President F -
301 Smith Treasurer M 210
134 Gonzales - F 110
340 Johnson Secretary M -
Sample Data
589 Brown M 195
Quick Note
• An Entity Instance Chart is useful for logging sample attribute data.
73
IDENTIFY ATTRIBUTES
Identify attributes by examining interview notes and by asking the user
questions.
Attributes may appear in interview notes as:
• Descriptive words and phrases.
• Nouns.
• Prepositional phrases (e.g. Salary amount for each employee).
• Possessive nouns and pronouns (e.g. Employee's name).
Questions to Ask the User
• What information do you need to know or hold about entity x?
• What information would you like displayed or printed about entity x?
74
Identify Attributes - cont'd
Examine documentation on existing manual procedures or automated systems to discover additional
attributes and omissions.
Paper Forms Computer Reports Computer Files
Headings
Fields
Record layouts
Prompts
Headings
File Dumps
Sort Orders
Questions to Ask the User
• Is this attribute really needed?
Quick Notes
• Beware of obsolete requirements left over from previous systems.
• Beware of derived data.
For further information on the subject see:
CASE*Method Entity Relationship Modelling, 5456-V1.0, pp. 5-6 and 5-7.
75
EXERCISE 3-7
Develop an E-R Diagram.
1. Develop an E-R Diagram for the following situation. Be sure to tag each attribute with its
optionality.
"Our regional Oracle User's Group has grown to include over 200 members. We're an all
volunteer organization, and our records are a mess. We need an information system to help us
keep track of all our affairs.
We definitely need to automate our membership records. For each member, we need to keep the
member's name, title, mailing address, office phone number, type of membership (individual or
corporate), and whether or not the member is current on dues. We collect dues on a yearly basis,
and everyone's dues are due in January.
We also like to know which company a member works for, but keeping this information current
is a real chore because our members are always changing companies. We only try to track a
single current employer for each member. Our members come from many different companies
including Coors, EG&G, and Storage Tech. A few of our members are unemployed. For each
company, we keep the company name, address, and type of business. We have a standard set of
type of business codes. We only keep the main company address for each company.
We hold various events during the year, and we'd like to track information about each event.
Some of our annual events include the September Meeting, the November Meeting, the annual
Training Day in January, and our April Meeting. We also hold specia l events each year. For
example, we held a special CASE day last May, and Richard Barker from ORACLE U.K. came
and spoke. We hold our events at several different locations around town including AT&T,
Redrocks Community College, and D.U. We'd like to track each event's date, an optional
description of the event, number of attendees, where it was held, how much money we spent on
it, and any comments on the event. We treat all comments as if they came from an anonymous
submitter. A set of comments is just a free form text statement of any length. We number each
set of comments, and we frequently get multiple sets of comments for an event.
We also track which members attended which events. Some of our members are really active,
and others attend very infrequently or just enjoy receiving our newsletter.
(continued)
76
Exercise 3-7 - cont'd
"We also need to track what type of computer platforms our members are using. We have a
unique, three-digit system identification tag for each type of platform. For example, 001 is for
IBM/MVS; 002 is for IBM/VM; 003 is for VAX/VMS; 020 is for OS/2; 030 is for PC/DOS:
050 is for Sun Unix; and 080 is for other Unix platforms.
We also like to track which application areas each member is interested in. For example,
accounting, human resources, oil and gas, pharmaceuticals, and health systems. The
applications should be portable, so we don't need to know which platforms they run on."
77
ASSIGN UNIQUE IDENTIFIERS
A Unique Identifier (UID) is any combination of attributes and/or
relationships that serve to uniquely identify an occurrence of an entity.
Each entity occurrence must be uniquely identifiable.
Example
In a business, each occurrence of DEPARTMENT is uniquely identified by its department number.
The UID for the entity DEPARTMENT is the attribute number.
Example
For a small theatre, each ticket is uniquely identified by its date of performance and its seat number.
The UID for the entity THEATRE TICKET is the combination of the two attributes date of performance and seat number.
An entity must have a UID, or it is not an entity.
Quick Notes
• All components of a UID must be mandatory *.
• Tag each UID attribute with #*.
78
Assign Unique Identifiers - cont'd
An entity can be uniquely identified through a relationship.
Example
In the banking industry, each bank is assigned a unique bank number. Within a bank, each account has
a unique account number. What is the UID of the entity ACCOUNT?
ACCOUNT is uniquely identified by its attribute number and the specific BANK the account is related to.
Use a UID bar to indicate that a relationship is part of the entity's UID.
Example
The UID bar indicates that the relationship with BANK is part of the UID of ACCOUNT.
Quick Note
• A relationship included in a UID must be mandatory and one and only one in the direction that
participates in the UID.
79
Assign Unique Identifiers - cont'd
An entity may be uniquely identified through multiple relationships.
Example
A business needs to track the work assignments of its employees. Employees are given work
assignments to projects. An employee may be given multiple assignments to a single project, each
with a different date of assignment.
What is the UID of the entity WORK ASSIGNMENT?
A WORK ASSIGNMENT is uniquely identified by the EMPLOYEE the WORK ASSIGNMENT is for, the PROJECT the WORK ASSIGNMENT is to, and the date assigned.
Quick Note
• Both relationships are mandatory and one and only one in the direction included in the UID.
80
Assign Unique Identifiers - cont'd
An entity may have more than one UID.
Example
What uniquely identifies an EMPLOYEE?
Candidate UIDs include:
1. badge number
2. payroll number
3. first name/last name
Are they all unique? The first name/last name combination is probably not unique.
Select one candidate UID to be the primary UID, and the others to be
secondary UIDs.
Quick Notes
• Either tag Secondary UIDs as (#), or do not tag them.
• CASE*Dictionary can document multiple secondary UIDs.
81
Assign Unique Identifiers - cont'd
Consider creating unique, artificial attributes to help identify each entity.
Example
What uniquely identifies a CUSTOMER entity?
Possibly the CUSTOMER'S first and last name could be a UID. However, there could be two CUSTOMERS with the same name.
Create an artificial attribute called CUSTOMER code which will be unique for each instance of
CUSTOMER.
Quick Notes
• Artificial attributes are used often for UIDs.
• Define an artificial code when the business does not have a natural attribute which uniquely
identifies an entity.
82
Assign Unique Identifiers - cont'd
Search for attributes and relationships to identify each entity.
Evaluate the Attributes
• What mandatory attributes identify the entity? Seek out additional attributes that help identify
the entity. Consider creating artificial attributes for identification.
• Does an attribute uniquely identify the entity?
• What combinations of attributes uniquely identify the entity?
Consider the Relationships
• Which of the relationships help identify the entity?
• Are there missing relationships that help identify the entity?
• Does the relationship help uniquely identify the entity?
• Is the relationship mandatory and one and only one in the direction from the entity?
Validate the UID
• Examine sample data. Does the selected combination of attributes and relationships uniquely
identify each instance of an entity?
• Are all the attributes and relationships that are included in the UID mandatory?
83
EXERCISE 3-8
Identify UIDs.
1. For the Training Company situation and E-R model from Exercise 3-5, supply attribute tags
for each attribute, and identify a UID for each entity. Add these attribute tags and UID's to the
E-R model.
"I'm the manager of a training company that provides instructor-led courses in management
techniques. We teach many courses, each of which has a code, a name, and a fee. Introduction
to UNIX and C Programming are two of our more popular courses. Courses vary in length from
one day to four days. An instructor can teach several courses, Paul Rogers and Maria Gonzales
are two of our best teachers. We track each instructor's name and phone number. Each course is
taught by only one instructor. We create a course and then line up an instructor. The students
can take several courses over time, and many of them do this. Jamie Brown from AT&T took
every course we offer! We track each student's name and phone number. Some of our students
and instructors do not give us their phone numbers."
E-R Model from Exercise 3-5
84
EXERCISE 3-9
Identify UIDs.
1. For the Video Store situation and E-R Model from Exercise 3-6, identify a UID for each entity
and add these UIDs to the E-R model. Also, supply attribute tags for each attribute.
"I'm the owner of a small video store. We have over 3,000 video tapes that we need to keep
track of.
Each of our video tapes has a tape number. For each movie, we need to know its title and
category (e.g. comedy, suspense, drama, action, war, or sci-fi). Yes, we do have multiple copies
of many of our movies. We give each movie a specific id, and then track which movie a tape
contains. A tape may be either Beta or VHS format. We always have at least one tape for each
movie we track, and each tape is always a copy of a single, specific movie. Our tapes are very
long, and we don't have any movies, which require multiple tapes.
We are frequently asked for movies starring specific actors. John Wayne and Katherine
Hepburn are always popular. So we'd like to keep track of the star actors appearing in each
movie. Not all of our movies have star actors. Customers like to know each actor's "real" birth
name and date of birth. We track only actors who appear in the movies in our inventory.
We have lots of customers. We only rent videos to people who have joined our "video club." To
belong to our club, they must have good credit. For each club member, we’d like to keep his or
her first and last name, current phone number, and current address. And, of course each club
member has a membership number.
Then we need to keep track of what video tapes each customer currently has checked out. A
customer may check out multiple video tapes at any given time. We just track current rentals.
We don't keep track of any rental histories."
85
Exercise 3-9 - cont'd
E-R Model from Exercise 3-6
86
EXERCISE 3-10
Identify UIDs.
1. For the Oracle User's Group situation and E-R Model from Exercise 3-7, identify a UID for
each entity and add these UIDs to the E-R Model.
"Our regional Oracle User's Group has grown to include over 200 members. We're an all-
volunteer organization, and our records are a mess. We need an information system to help us
keep track of all our affairs.
We definitely need to automate our membership records. For each member, we need to keep the
member's name, title, mailing address, office phone number, type of membership (individual or
corporate), and whether or not the member is current on dues. We collect dues on a yearly basis
and everyone's dues are due in January.
We also like to know which company a member works for, but keeping this information current
is a real chore because our members are always changing companies. We only try to track a
single current employer for each member. Our members come from many different companies
including Coors, EG&G, and Storage Tech. A few of our members are unemployed. For each
company, we keep the company name, address, and type of business. We have a standard set of
type of business codes. We only keep the main - company address for each company.
We hold various events during the year, and we'd like to track information about each event.
Some of our annual events include the September Meeting, the November Meeting, the annual
Training Day in January, and our April Meeting. We also hold special events each year. For
example, we held a special CASE day last May, and Richard Barker from ORACLE U.K. came
and spoke. We hold our events at several different locations around town including AT&T.
Redrocks Community College, and D.U. We'd like to track each event's date, an optional
description of the event, number of attendees, where it was held, how much money we spent on
it, and any comments on the event. We treat all comments as if they came from an anonymous
submitter. A set of comments is just a free form text statement of any length. We number each
set of comments, and we frequently get multiple sets of comments for an event.
We also track which members attended which events. Some of our members are really active,
and others attend very infrequently or just enjoy receiving our newsletter.
(continued)
87
Exercise 3-10 - cont'd
We also need to track what type of computer platforms our members are using. We have a
unique, three-digit system identification tag for each type of platform. For example, 001 is for
IBM/MVS; 002 is for IBM/VM; 003 is for VAX/VMS; 020 is for OS/2; 030 is for PC/DOS;
050 is for Sun Unix;, and 080 is for other Unix platforms.
"We also like to track which application areas each member is interested in. For example,
accounting, human resources, oil and gas, pharmaceuticals, and health systems. The
applications should be portable, so we don't need to know which platforms they run on."
E-R Model from Exercise 3-7
88
REVIEW: BASIC CONCEPTUAL DATA MODELLING
An entity is a thing of significance about which information needs to be
known or held.
Diagramming Conventions
• Soft box
• Singular, unique name
• Name in upper case
• Optional synonym name (in parentheses)
• Any dimensions
Identify and Model Entities
1. Examine the nouns. Are they things of significance?
2. Name each entity.
3. Is there information of interest about the entity that the business needs to hold?
4. Is each instance of the entity uniquely identifiable? Which attribute or attributes could serve as
its UID?
5. Write a description of it. "An EMPLOYEE has significance as a paid worker at the company.
For example, John Brown and Mary Smith are EMPLOYEES."
6. Diagram each entity and a few of its attributes.
89
Review: Basic Conceptual Data Modelling - cont'd
A relationship is a two-directional, significant association between two entities, or between an entity
and itself.
Relationship Syntax
Diagramming Conventions
Crows always fly east or south!
Analyze and Model the Relationships Between Entities
1. Determine the existence of a relationship.
2. Name each direction of the relationship.
3. Determine the optionality of each direction of the relationship.
4. Determine the degree of each direction of the relationship.
5. Model the relationship.
90
Review: Basic Conceptual Data Modelling - cont'd
Attributes are information about an entity that needs to be known or held.
Diagramming Conventions
• Attribute names are singular, lower case, and do not include the entity's name.
• Attribute tags: * for mandatory and o for optional.
Analyze and Model Attributes
1. Identify a candidate attribute.
2. Associate the attribute with an entity.
3. Name the attribute.
4. Determine the optionality of the attribute.
5. Validate that the attribute is really an attribute and not an entity.
6. Break down aggregate attributes.
7. Verify that an attribute is single valued.
8. Verify that an attribute is not derived.
91
Review: Basic Conceptual Data Modelling - cont'd
Each entity must be uniquely identifiable. A Unique Identifier (UID) is any
combination of attributes and/or relationships that serve to uniquely
identify an occurrence of an entity.
Diagramming Conventions
• # indicates an attribute is part of an entity's UID.
• The UID bar indicates a relationship is part of the UID.
Identify UIDs for Each Entity
1. Seek out candidate attributes that help identify an entity.
2. Determine the entity's dependence upon other related entities.
3. Define the UID for the entity.
92
4
ADVANCED
CONCEPTUAL DATA MODELLING
93
SECTION OBJECTIVES
At the end of this section, you will be able to:
1. Validate that an attribute is properly placed based upon its dependence on its entity's UID.
2. Resolve many-to-many relationships with intersection entities.
3. Identify and model advanced data constructs including recursive relationships, subtypes, and
exclusive relationships.
94
NORMALIZE THE DATA MODEL
Normalization is a relational database concept, but its principles apply to
Conceptual Data Modelling.
Validate each attribute's placement using the rules of normalization.
Normal Form Rule Description
First Normal Form (1NF) All attributes must be single -valued
Second Normal Form (2NF) An attribute must be dependent upon its entity's entire unique
identifier.
Third Normal Form (3NF) No non-UID attribute can be dependent on another non-UID
attribute.
A normalized entity-relationship data model automatically translates into a
normalized relational database design.
Quick Notes
• Third normal form is the generally accepted goal for a database design that eliminates
redundancy.
• Higher normal forms are not widely used.
95
Normalize the Data Model - cont'd
First Normal Form Rule: All attributes must be single-valued.
Validation Check:
• Validate that each attribute has a single value for each occurrence of the entity. No attribute
should have repeating values.
Example
Does the entity CLIENT comply with 1NF? If not, how could it be converted to 1NF?
The attribute date contacted has multiple values, therefore the entity CLIENT is not in 1NF Create an additional entity CONTACT with a M:1 relationship to CLIENT.
If an attribute has multiple values, create an additional entity and relate it
to the original entity with a M:1 relationship.
96
Normalize the Data Model - cont'd
Second Normal Form Rule: An attribute must be dependent upon it entity's
entire unique identifier.
Validation Check:
• Validate that each attribute is dependent upon its entity's entire unique identifier. Each specific
instance of the UID must determine a single instance of each attribute.
• Validate that an attribute is not dependent upon only part of it's entity's UID.
Example
Validate the placement of the COURSE entity's attributes.
Each instance of a course code determines a specific value for name duration and fee. The attributes are properly placed.
Example
Validate the placement of the attributes for the ACCOUNT and BANK entities.
Each instance of a BANK and account number determine specific values of balance and date opened for each account. The attribute bank location is misplaced. It is dependent on BANK, but not on account number. It should not be an attribute of ACCOUNT.
If an attribute is not dependent on its entity's entire UID, it is misplaced
and must be moved.
97
Normalize the Data Model - cont'd
Third Normal Form Rule: No non-UID attribute can be dependent on
another non-UID attribute.
Validation Checks:
• Validate that each non-UID attribute is not dependent upon another non-UID attribute.
• Move any non-UID attribute that is dependent upon another non-UID attribute.
Example
Are any of the non-UID attributes for this entity dependent upon another non-UID attribute?
The attributes customer name and state are dependent upon the customer id. Create another entity called CUSTOMER with a UID of customer id, and place the attributes accordingly.
Quick Note
• If an attribute is dependent upon a non-UID attribute, move both the dependent attribute and
the attribute it is dependent upon to a new, related entity.
98
EXERCISE 4-1
Normalize an E-R Model
1. For the following E-R Model, evaluate each entity against the rules of normalization, identify
the misplaced attribute, and explain what rule of normalization each misplaced attribute
violates.
2. Optionally, re-draw the E-R diagrams in third normal form.
99
RESOLVE M:M RELATIONSHIPS
Attributes may seem to be associated with a M:M Relationship. Resolve
that M:M relationship by adding an intersection entity with those
attributes.
Example
Consider the M:M relationship between PRODUCT and VENDOR. What is the current price of a
specific PRODUCT from a specific VENDOR?
current price seems to be an attribute of the relationship between PRODUCT and VENDOR.
Attributes only describe entities. If attributes describe a relationship, the
relationship must be resolved.
100
Resolve M:M Relationships - cont'd
Replace or resolve a M:M Relationship with a new Intersection Entity and
two M:1 relationships.
Example
The M:M relationship between PRODUCT and VENDOR can be resolved by adding the intersection
entity CATALOG ITEM. Current price is really an attribute of the entity CATALOG ITEM.
Once the entity CATALOG ITEM is defined, the requirement for additional attributes of CATALOG ITEM surfaced: package quantity and unit of measure are also attributes of CATALOG ITEM. The UID for CATALOG ITEM is composed of its two relationships.
Quick Notes
• An Intersection Entity is frequently identified by its two originating relationships - note the
two UID bars.
• The relationships from the intersection entity are always mandatory.
• Intersection entities frequently represent real-world business entities.
• Intersection entit ies usually contain consumables like quantity used and dates. They tend to be
high volume and volatile entities.
101
Resolve M:M Relationships - cont'd
Position Intersection Entities to allow the crowsfeet to point up or to the
left.
M:M Relationship Layout
Intersection Entity Layout
Quick Notes
• A Reference Entity is an entity that has no mandatory rela tionship ends connected to it.
• When M:M relationships are resolved, the layout of the entire diagram may need to be
shuffled.
102
Resolve M:M Relationships - cont'd
The UID of an intersection entity is frequently composed of its relationships
to the two originating entities.
Example
Resolve the following M:M relationship to accommodate these additional requirements:
"Track the date each student enrolled in a course, the date the student completed the course, and
the student's grade."
Solution
Add the intersection entity ENROLLMENT and two M:1 relationships.
ENROLLMENT has attributes of date enrolled, date completed, and grade. The UID of ENROLLMENT is made up of its relationships to STUDENT and COURSE.
Quick Note
• This model only tracks the last date the student enrolled in a specific course. If multiple
enrollments need to be kept, include the attribute date enrolled as part of the UID.
103
Resolve M:M Relationships - cont'd
An intersection entity's relationships to the two originating entities may not
be adequate to uniquely define each occurrence of the intersection entity.
Example
Resolve the following M:M relationship to accommodate these additional requirements:
"Track the date each employee is assigned to a project, and the duration of that assignment."
Add an intersection entity called WORK ASSIGNMENT with attributes date assigned and duration.
WORK ASSIGNMENT is partially identified by its relationships to EMPLOYEE and PROJECT, but
those two relationships are not enough to uniquely identify a WORK ASSIGNMENT. An employee
may have multiple assignments to a project, with different assignment dates. Therefore, the UID of
WORK ASSIGNMENT must include the related EMPLOYEE, the related PROJECT, and the
attribute date assigned.
104
Resolve M:M Relationships - cont'd
Once an intersection entity is identified, search for additional attributes
which describe the intersection entity.
Example
What information needs to be known about the relationship between PRODUCT and VENDOR? "We
need to track the current price of a specific PRODUCT from a specific VENDOR.
Resolve the following M:M relationship to accommodate this additional requirement.
Add the intersection entity VENDOR ITEM with an attribute of current price.
What other information needs to be known about a VENDOR ITEM?
"We also need to know the package quantity and unit of measure of each VENDOR ITEM."
105
Resolve M:M Relationships - cont'd
Search for attributes which identify, or help to identify an intersection
entity.
Example
How do you identify each VENDOR ITEM? Do you use the combination of the related VENDOR
code and the PRODUCT id?
"No, we have a catalog of all orderable VENDOR ITEMs, and each VENDOR ITEM has a unique
catalog number."
According to the rules of the business, each VENDOR ITEM has a unique catalog number. So the
attribute catalog number should be the UID of VENDOR ITEM.
106
Resolve M:M Relationships - cont'd
Resolve all M:M relationships by the end of the Analysis phase. This forced
resolution may result in an Intersection Entity with no attributes.
Example
In the Video Store situation, the following M:M relationship was defined.
At the end of the Analysis Stage, the user has not identified any attributes that are associated with the
M:M relationship. Resolve the M:M relationship with an Intersection Entity with no attributes.
Quick Notes
• An Intersection Entity with no attributes is just a two-way cross-reference list between occurrences of the entities.
• An Intersection Entity with no attributes is the exception to the rule that an entity must have attributes to be an entity.
• The UID for an empty Intersection Entity is always composed of the relationships of the two entities from which it or iginated.
107
EXERCISE 4-2
Resolve a M:M relationship.
1. In the E-R Model for the Oracle User's Group from Exercise 3-10, a M:M relationship was
initially modelled between the MEMBER entity and the APPLICATION AREA entity.
Resolve that M:M relationship based upon the following additional requirements.
Additional Requirements
"We would also like to keep a brief description of each member's interest in each specific
application area. For example, one member might already have a large accounting application
system that they developed in house. Another member might be interested in an application area
without describing that interest."
108
EXERCISE 4-3
Resolve a M:M relationship.
1. Resolve the following M:M Relationship between CUSTOMER and PRODUCT. Add the
attributes date ordered, quantity ordered, and price.
109
MODEL HIERARCHICAL DATA
Represent hierarchical data as a set of many to one relationships.
Example
Model a company's hierarchical organization structure as a set of M:1 relationships.
Quick Note
• Oracle's E-R Diagram layout rule Crows fly east or south causes hierarchies to be drawn
upside-down or sideways!
110
Model Hierarchical Data - cont'd
The UID's for a set of hierarchical entities may be propagated through
multiple relationships.
Example
What are the UIDs of the entities FLOOR, SUITE, and ROOM?
The UID of ROOM is the room id and the SUITE it is located within. The UID of SUITE is the suite number and the FLOOR it is located on. The UID of FLOOR is the floor number and the BUILDING it is contained in.
111
Model Hierarchical Data - cont'd
Consider creating artificial attributes to help identify entities in a
hierarchical relationship.
Example
In a typical organization structure, what could uniquely identify instances of the entities DIVISION,
DEPARTMENT, and TEAM?
Each TEAM could be identified based upon its DEPARTMENT, DIVISION, and COMPANY. Or
each entity could have a unique, independent, artificial identification code.
Quick Notes
• Unique, independent, artificial identification codes tend to be shorter in length.
• If the hierarchical structure changes often, use independent artificial identifiers.
112
MODEL RECURSIVE RELATIONSHIPS
A Recursive Relationship is a relationship between an entity and itself.
Example
Read the recursive relationship in the following E-R Diagram.
Each EMPLOYEE may be managed by one and only one EMPLOYEE. Each EMPLOYEE may be the manager of one or more EMPLOYEES.
Quick Notes
• The E-R diagramming convention that shows a recursive relationship is known as a pig's ear.
• The loop can appear on any side of the entity's box, but remember that crows always fly east
or south.
113
Model Recursive Relationships - cont'd
Consider representing a hierarchy as a recursive relationship.
Example
A business hierarchy can be drawn as a recursive relationship.
Quick Notes
• The single recursive entity must include all of the attributes of each individual entity. Ideally, the entities at each level of the hierarchy would have the same attributes.
• A recursive organization model can readily accommodate the addition or subtraction of organization layers.
• A recursive organization model cannot handle a mandatory relationship. If each ORGANIZATION ELEMENT must be within another ORGANIZATION ELEMENT, the organization hierarchy would have to be infinite.
• A recursive relationship must be optional in both directions.
114
Model Recursive Relationships - cont'd
Bill of Materials data can be modelled with multiple entities for each
category of "part" and a set of relationships between each of those entities.
Example
An automobile manufacturing organization needs to track elementary parts, subassemblies,
assemblies, and products. The following E-R diagram models this data by considering each of these
part categories as an entity.
115
Model Recursive Relationships - cont'd
Model Bill of Materials data as a many to many recursive relationship.
Example
For the automobile manufacturing organization, consider all elementary parts, subassemblies,
assemblies, and products as instances of an entity called COMPONENT. Then the previous complex
E-R Model can be remodelled as a simple recursive relationship.
Each COMPONENT may be a part of one or more COMPONENTS. Each COMPONENT may be made up of one or more COMPONENTS.
116
Model Recursive Relationships - cont'd
Resolve a recursive M:M relationship with an intersection entity and two
M:1 relationships to different instances of the original entity.
Example
Consider the recursive model of a Bill of Materials structure. This model will track information about
which components are part of a fan. But if a washer is part of a fan, will it also track how many
washers are parts of a fan?
The attribute quantity seems to be associated with the recursive relationship.
Resolve this M:M recursive relationship by adding the intersection entity ASSEMBLY RULE and two
M:1 relationships back to the COMPONENT entity. ASSEMBLY RULE will have an attribute of
quantity.
The two M:1 relationships from an instance of ASSEMBLY RULE will be associated with different instances of the COMPONENT entity. For example, the ASSEMBLY RULE instance for washers to fan will have a M:1 relationship to the COMPONENT instance for washer and a second M:1 relationship to the COMPONENT instance for fan. The ASSEMBLY RULE entity will record the quantity of washers, which are a part of a single fan.
117
EXERCISE 4-4
Model hierarchical and recursive relationships.
1. Develop two E-R diagrams to represent the following situation. Develop one as a hierarchical
structure, and one as a recursive structure.
"Our company sells products throughout the United States. So we've divided the U.S. into four
major sales regions: the Northern, Eastern, Southern, and Western Regions. Each sales region
has a unique region code. Each sales region is then divided into sales districts. For example, the
Western Region is divided into the Rocky Mountain, Northwest, Pacific Coast, and Pacific
Districts. Each district has a unique district code.
Each district is made up of sales territories. The Rocky Mountain District is composed of three
territories: Wyoming-Montana, Colorado, and Utah-New Mexico. The northwest District is
made up of two territories: The Washington and Oregon-Idaho territories. The Pacific Coast
District is composed of two territories: the California and Nevada territories. The Pacific
District includes the Hawaii territory and the Alaska territory. Each territory has a unique
territory code.
Then each sales territory is broken down into sales areas. For example, Colorado is made up of
two sales areas: the Front Range and the Western Slope sales areas. Each sales area has a unique
sales area code.
Each salesperson is responsible for one or more sales areas, and has a specific sales quota. We
also have sales managers who are responsible for one or more sales districts, and sales directors
who are responsible for one or more sales regions. Each sales manager is responsible for the
territories within his districts. We don't overlap our employees' responsibilities - a sales area is
always the responsibility of a single salesperson, and our managers and director's
responsibilities don't overlap. Sometimes our salespersons, managers, and directors will be on
leave or special assignments arid will not have sales turf responsibilities. We identify all our
sales personnel by their employee ids."
118
MODEL ROLES WITH RELATIONSHIPS
Beware of entities that represent roles.
Example
In the E-R Model for the Training Company, we defined an INSTRUCTOR entity and a STUDENT
entity. This model works fine if an INSTRUCTOR is never a STUDENT, and a STUDENT is never
an INSTRUCTOR. But what if an INSTRUCTOR is also a STUDENT?
Entities, which represent roles, may share overlapping instances.
119
Model Roles with Relationships - cont'd
Use relationships to model roles. Relationships allow a single entity instance
to assume multiple roles.
Example
For the Training Company, define a PERSON entity, which may take on the roles of instructor and/or
student.
120
MODEL SUBTYPES
Use subtypes to model exclusive entity types which have common attributes
and common relationships.
Example
"A business has defined two types of employees: exempt and non-exempt. For all employees, track
each employee's badge number, first name, last name, and assigned department. For the exempt
employees, also track employee salary. For the non-exempt employees, track the employee's hourly
rate, overtime rate, and membership in a union."
Create an EMPLOYEE supertype with two subtypes. Each EMPLOYEE is either an EXEMPT
EMPLOYEE or a NON-EXEMPT EMPLOYEE.
Quick Note
• Beware of instances that could be both subtypes - the subtype/supertype construct is incorrect
in those instances.
121
Model Subtypes - cont'd
A supertype is an entity that has subtypes. A supertype may be split into
two or more mutually exclusive subtypes.
Example
An EMPLOYEE is either an EXEMPT EMPLOYEE or a NON-EXEMPT EMPLOYEE, but not both.
A supertype may have attributes and relationships shared by its subtypes.
Example
All EMPLOYEES must have the attributes badge number, first name, and last name. All EMPLOYEES
must be assigned to one and only one DEPARTMENT.
Each subtype may have its own attributes and relationships.
Example
The EXEMPT EMPLOYEE subtype has an attribute of salary.
The NON-EXEMPT EMPLOYEE subtype has attributes of hourly rate and overtime rate, and a
relationship with the entity UNION.
Quick Note
• A subtype with no attributes or relationships of its own may be a synonym for the supertype
entity and not a subtype.
122
Model Subtypes - cont'd
All instances of the supertype entity must belong to one and only one of the
subtype entities. Subtypes must form a complete set with no overlaps.
Example
In general, a job is either a MANUAL JOB or a CLERICAL JOB, but there might be a few excep-
tions.
Supertype Reading Rules
"Each supertype entity must be either a subtype 1 or a subtype2"
Example
"Each JOB must be either a MANUAL JOB, a CLERICAL JOB, or OTHER JOB."
Subtype Reading Rules
"...subtype, which is a type of supertype,..."
Example
"...CLERICAL JOB, which is a type of JOB,..."
Always use the subtype OTHER when unsure about the set's completeness.
123
Model Subtypes - cont'd
Subtypes can be further subtyped. Normally two or three levels of nesting
are adequate.
Example
Define further subtypes for the subtype entity AIRPLANE.
AIRPLANE is a subtype of AIRCRAFT and a supertype of POWERED AIRPLANE and GLIDER.
JET PLANE inherits the attributes and relationships of POWERED AIRPLANE, AIRPLANE, and AIRCRAFT.
124
MODEL EXCLUSIVE RELATIONSHIPS
Model two or more mutually exclusive relationships from the same entity
using an arc.
Example
A BANK ACCOUNT either must be owned by an INDIVIDUAL or must be owned by a COMPANY.
Use an arc to model this relationship.
Exclusive Relationship Reading Rules
"Each entityA either relationship1 entity1 or relationship2 entity2."
Example
Each BANK ACCOUNT either must be owned by one and only one INDIVIDUAL or must be owned
by one and only one COMPANY.
Arc Modelling Conventions
• The relationships in an arc frequently have the same relationship name.
• The relationships in an arc must be either all mandatory, or all optional.
• An arc belongs to a single entity, and must only include relationships originating from that entity.
• An entity may have multiple arcs, but a specific relationship can only participate in a single arc.
125
Model Exclusive Relationships - cont'd
Choose between two conventions for drawing arcs.
Drawing Convention 1 - An Arc with Optional Dots
A dot on the arc is used to signify that a relationship belongs to the arc.
Drawing Convention 2 - An Arc without Dots
Any relationship crossed by the arc belongs to the arc. A break in the arc indicates a relationship,
which is not included in the arc.
126
EXERCISE 4-5
Develop an E-R Model.
1. Develop an E-R Model for the following information requirements.
"The Right-Way Rental Truck Company rents small moving trucks and trailers for local and
one-way usage. We have 34 7 rental offices across the western United States. Our rental stock
includes a total of 5,780 vehicles including various types of trucks and trailers. We need to
implement a system to track our rental agreements and our vehicle assignments. Each rental
office rents vehicles that they have in stock to customers ready to take possession of the vehicle.
We don't take reservations, or speculate on when the customer will return rented vehicles. The
central office oversees the vehicle distribution, and directs transfers of vehicles from one rental
office to another.
Each rental office has an office name like "Littleton Right-Way." Each office also has a unique
three-digit office number. We also keep each office's address. Each office is a home office for
some of our vehicles, and each vehicle is based out of a single home office.
Each vehicle has a vehicle id, state of registration, and a license plate registration number. We
have five different types of vehicles: 36' trucks, 24' trucks, 10' trucks, 8' covered trailers, and 6'
open trailers. Yes, we do have a vehicle type code. For all our vehicles, we need to track the last
maintenance date, and expiration date of its registration. For our trucks, we need to know the
current odometer reading, the gas tank capacity, and whether or not it has a working radio. For
long moves, customers really prefer a radio. We log the current mileage just before we rent a
truck, and then again when it is returned.
Most of our rental agreements are for individual customers, but a rental agreement can either be
for an individual or for a company. We do rent a small percentage of our trucks to companies.
We assign each company an identifying company number and track the company's name and
address. No, we don't need to worry about any additional information about a company. Our
corporate sales group handles all that information separately.
(Continued)
127
Exercise 4-5 - cont'd
"For each individual customer, we record the customer's name. home phone, address, and
driver's license state, number, and expiration date. We like to keep track of all our customers. If
a customer damaged a vehicle, abandoned it, or didn't fully pay the bill, then we tag the
customer as a poor risk, and won't rent to that customer again.
We only allow a single individual or company for a given rental agreement, and we write a
separate rental agreement for each vehicle. Yes, we do have customers rent two or more
vehicles at the same time. Each rental agreement is identified by the originating rental office
number and a rental agreement number. We also need to track the rental date, the anticipated
duration of the rental, the originating rental office, the drop-off rental office, the amount of the
deposit paid, the quoted daily rental rate, and the quoted rate per mile. Of course for the trailers,
there isn't a mileage charge. No, we don't need to automate the financial side of our business,
just our rental agreement tracking and vehicle assignment functions."
128
MODEL DATA OVER TIME
Add additional entities and relationships to the E-R model to accommodate
historical data.
Ask the User:
• Is an audit trail required?
• Can attribute values change over time?
• Can relationships change over time?
• Do you need to query older data?
• Do you need to keep previous versions?
Quick Note
• Validate any requirements for storing historical data with the user. Storing unnecessary
historical data can be costly.
129
Model Data Over Time - cont'd
Create an additional entity to track an attribute's values over time.
Example
A consulting firm needs to keep information about its contracts. Each contract has a unique contract
id, and they need to keep a description of the contract, the contract's status (e.g. open, closed, or
suspended.) Initially the following CONTRACT entity was modelled.
The above CONTRACT entity supports a single current status value for CONTRACT. The law Firm
wants to track the dates each contract was opened, was closed, and was suspended. To model status
values over time add a STATUS entity.
The UID of the STATUS entity is the related CONTRACT and the effective date.
Quick Note
• Use a single entity to record the values over time of multiple attributes associated with an
entity (such as CONTRACT).
130
Model Data Over Time - cont'd
Add a new entity to accommodate a relationship that may change over
time.
Example
An apartment owner wants to track the tenants in each of his apartments. (The apartment only writes
rental contracts with a single person, not multiple people.) The following E-R Model will only track
the current renter of an APARTMENT.
Add the entity RENTAL HISTORY ENTRY to capture the values of the rental relationship over time.
131
Model Data Over Time - cont'd
An intersection entity is frequently used to track information about a
relationship, which changes over time.
Example
A professional society wants to track the companies that its members have been employed by over
time and the term of each employment (e.g. from date and to date). There is an M:M rela tionship
between each member and each company.
Add an intersection entity, EMPLOYMENT HISTORY ENTRY, to track each employee's em-
ployments over time and the dates of those employments.
By including the attribute from date in the UID of EMPLOYMENT HISTORY ENTRY, this model
will track any multiple terms of employment at a single company by a single employee.
132
EXERCISE 4-6
Model data over time.
1. Modify the Video Store E-R Model to accommodate the following additional requirements.
"You know, we really need to keep a history of all our rentals. Each time a customer rents a
tape, we would like to keep the rental date/time and the return date/time. All our tapes are due
back the next day, so we don't need to keep a due date.
Keeping this rental history will allow us to analyze the pattern of our rentals. We will be able to
determine how many tapes each customer rents and how many times a customer has returned a
tape late. We will also know how many times a particular tape has been used, and will then
know when to retire each tape. We will also be able to analyze our customers' movie
preferences."
133
MODEL COMPLEX RELATIONSHIPS
Beware of a ring of M:M relationships.
Example
Develop an E-R model for employment history. For each person, track the position held, the company
worked for, and the dates the posit ion was held. A person may hold a specific position within the same
company multiple times during their career. Initially the following E-R Model was defined.
The dates of the position seem to be an attribute of a relationship. So resolve each of the M:M
relationships.
Which intersection entity are the dates of the position attributes of? All of them? None of them?
134
Model Complex Relationships - cont'd
Model a relationship between three or more entities as an Intersection
Entity with mandatory relationships with those entities.
Example
A person's employment history is really a 3-way relationship between the PERSON, COMPANY, and
POSITION entities. Use a single intersection entity called EMPLOYMENT HISTORY to model this
relationship.
A complex relationship is a relationship between three or more entities.
Quick Notes
• An intersection entity for a complex relationship always has mandatory relationships back to
the entities to which it relates.
• For an intersection entity representing a complex relationship, follow the rules of basic E-R
Modelling to name the entity, and to analyze and model its relationships, its attributes, and its
UID.
• Consider its mandatory relationships as candidates for inclusion in its UID.
135
EXERCISE 4-7
Model a complex relationship.
1. In the E-R Model for the Oracle User's Group from Exercise 3-10, a M:M relationship was
initially modelled between the MEMBER entity and the COMPUTER PLATFORM entity.
Revise that relationship based upon the following revised requirements.
Revised Requirements
"No, we really don't need to know what computer platform each member is using. Instead, what
we really need to know is which Oracle products (RDBMS, Pro*C, SQL*Forms,
SQL*TextRetrieval, CASE, Financials, etc.) each member is using on which computer
platforms. No, we don't need to keep the specific version of each product, just the general
product name."
136
EXERCISE 4-8
Optional Exercise
Develop a complex E-R Model.
1. Develop an E-R Model for the following business.
"I am the senior partner in a large, diversified law firm. My firm Bailey and Associates, handles
a wide variety of cases including traffic violations, domestic disputes, civil suits, and homicide
cases.
We have retained a database administrator to organize and track various data because the firm
grew faster than we had imagined and now there are "cases lying all over the place."
Our firm is made up of departments such as litigation, homicide, etcetera, and each case is
assigned to a particular department for administrative purposes. Attorneys are also assigned to a
particular department, but this is only for billing/payroll purposes since an attorney can work on
cases in other departments.
We need a list of events for a given case (essentially a history of the case) that includes a log of
events and the date the event became effective, Cases have to be identifiable by a unique
number which appears on a list with every event date and event description. Events have special
codes like O for Open, T for Trial, L for Lost, and there must always be an event status for
every case.
We want to keep track of important information associated with a case including the department
to which it is assigned and a brief description (such as Jones vs. Jones). After a case has been
closed, it may be reopened at some future date. We assign reopened cases new case numbers,
but we need to tie the new case number to the previous case number.
(continued)
137
Exercise 4-8 - cont'd
Attorneys can be party to multiple cases the same way a number of people can be party to
multiple cases. For example, Jones may be a judge on one case and an eyewitness on another.
We are only interested in keeping track of parties and the roles that they play in the context of a
particular case. Parties should be identified by their name and date of birth, and some kind of
unique numbering system.The kinds of people that may be involved in cases include judges
(JG), eyewitnesses (EW), defendants (DE) and of course attorneys (AT). For example, we have
a murder case, and we're working for the defendant.One attorney is assigned to the case, and
there is, of course, a judge presiding over the case. There is also an eyewitness. Thus, there are
four people who are parties to this case, and we'd like to know about all four. In this context, we
are not tracking the attorney in terms of billing, but simply as party to a case.
To elaborate on the varying roles that people can play, assume that a given party can serve in
different roles in different cases, but a party can only serve in one role on a given case."
138
EXERCISE 4-9
Optional Exercise
Develop a complex E-R Model.
1. Develop an E-R Model for the following business.
"I'm Phil Sales with Shipmore Cruises. We've decided that our manual system of booking
passengers onto our ships won't hold up when we get our new ship. so I guess that's why you're
here. Yes. we'll have two ships, no not boats, boats can fit onto ships, and we'll probably expand
to 5 or 6 by 1995. Each one has the name "Goodsea," "Goodwind," and the new one.
"Goodsky," and each one has a specific passenger capacity and registry. Registry is the country
that it is registered with. No. we don't need to worry about tonnage or draft or anything else
about the ship.
Each year we put out a brochure with the information on each cruise that we offer. Every cruise
has a name, length in number of days - huh? Oh, three, seven, eleven and fourteen day cruises.
Each cruise also has a specific ship assigned to it, some people want to go on only the newer
ships. Yes, I guess we would need the age of each ship. So, for each cruise we also have
different ports that we stop at. A three day cruise will have only one stop, always on the second
day of the cruise, a seven day cruise will stop at three ports, and so on. We vary ports depending
on where the cruise originates. What? The ports of Los Angeles, CA. and Miami, FL, as well as
Anchorage, AK. See. the LA cruises go down to Mexico ports like Cabo San Lucas and Mexico
City; the Miami cruises go to the Bahamas and the Virgin Islands: and the Anchorage cruises
make stops all through Alaska. Depending upon the length of each cruise, each cruise will make
port calls on different days out.
Passengers who sail with us will pick a given cruise, which has a certain length and number of
ports, and which cruise they pick will tell us which cabins are available. Once they choose from
what is available, we can then price them. That depends on the number of people in the cabin
and the "class" of the cabin. Huh? Whenever we book a cabin under the manual system we
remove the cabin from the availability board, unless it's not full and that passenger wants to
share with someone else. If the cabin can hold four people, and they are travelling alone, then
it's gonna cost 'em more. Once passengers are booked, and we get a deposit from them, then we
can pay the travel agent who made the reservation their commission."
139
5
RELATIONAL
DATABASE CONCEPTS
140
SECTION OBJECTIVES
At the end of this section, you will be able to:
• Understand what a relational database is.
• Define what primary keys and foreign keys are.
• Understand the concept of data integrity.
141
RELATIONAL DATABASE OVERVIEW
A relational database is a database that is perceived by the user as a
collection of relations or two-dimensional tables.
Example
The relational table below contains employee data.
Quick Notes
• Relational database tables are simple but disciplined.
• A relational database must possess data integrity, i.e., its data must be accurate and consistent.
142
Relational Database Overview - cont'd
Relational databases are manipulated a set at a time rather than a record at
a time.
Example
To select all employees who work in Department 10, use the following SQL statement.
SQL> SELECT emp_no, lname, fname, dept_no 2 FROM employee 3 WHERE dept_no = 10;
EMP_NO LNAME FNAME DEPT_NO ------ ----- ----- ------- 100 SMITH JOHN 10 210 BROWN JIM 10
The Structured Query Language (SQL) is used to manipulate relational
databases.
Quick Notes
• The American National Standards Institute (ANSI) has established SQL as the standard
language for operating upon relational databases.
• A relational database can support a full set of relational operations. Relational operations
manipulate sets of data values. Tables can be operated on to create other tables. Rela tional
operations can be nested.
143
PRIMARY KEYS
A Primary Key (PK) is a column or set of columns that uniquely identifies
each row in a table. Each table must have a primary key, and a primary
key must be unique.
Example
The primary key for the EMPLOYEE table consists of the EMP_NO column. Each row in the table is
uniquely identified by its EMP_NO value.
Quick Notes
• No duplicates are allowed in a Primary Key. The primary key must be unique.
• Primary keys generally cannot be changed.
• An entity's UID will map to a Primary Key in its corresponding table.
144
Primary Keys - cont'd
A Primary Key consisting of multiple columns is called a Composite
Primary Key or a Compound Primary Key.
Example
The composite primary key for the ACCOUNT table consists of the combination of the BANK_NO
and ACCOUNT_NO columns. Each row in the table is uniquely identified by its BANK NO and
ACCOUNT NO values.
Quick Note
• The columns of a composite primary key must be unique in combination. The individual
columns can have duplicates, but in combination, no duplicates are allowed.
145
Primary Keys - cont'd
No part of a primary key may be NULL.
Example
EMP_NO is the primary key of the EMPLOYEE table. Therefore EMP_NO must be defined as NOT
NULL.
Example
How does the ACCOUNT table violate the rules of Primary Keys?
Two of the rows contain NULL values in part of the composite PK. Both BANK_NO and ACCOUNT_NO must be defined as NOT NULL.
146
Primary Keys - cont'd
A table can have more than one column or combination of columns that can
serve as the table's primary key. Each of these is called a Candidate Key.
Example
What are the candidate keys for the EMPLOYEE table?
EMP_NO and PAYROLL_ID are candidate keys.
Select one candidate key to be the Primary Key for the table. The other
candidates become Alternate Keys (or Unique Keys).
Example
Quick Notes
• All Candidate Keys must be Unique and NOT NULL.
• Secondary UIDs map to Alternate Keys.
• Person names are not normally candidate keys because their uniqueness cannot be guaranteed.
For example, in the EMPLOYEE Table, the combination LNAME/ FNAME would probably
not be a candidate key.
FOREIGN KEYS
A Foreign Key (FK) is a column or combination of columns in one table
that refers to a primary key in the same or another table.
Example
DEPT_NO is a FK in the EMPLOYEE Table, and refers to values in the DEPT_NO column of the
DEPARTMENT Table.
Quick Notes
• Foreign keys are used to join tables.
• Foreign keys are based on data values and are purely logical.
Foreign Keys - cont'd
A foreign key must match an existing primary key value (or else be NULL).
Example
The FK DEPT_NO in the EMPLOYEE table refers to values of the PK DEPT_NO in the DEPART-
MENT table.
If a Foreign Key is part of a Primary Key, that FK cannot be NULL.
Example
In the ACCOUNT table, the FK BANK_NO must be NOT NULL because it is part of the PK.
DATA INTEGRITY
Data Integrity refers to the accuracy and consistency of the data.
Data Integrity Constraints
Data integrity constraints define the relationally correct state for a database.
Data integr ity constraints ensure that users perform only operations which leave the database in a
correct, consistent state.
Constraint Type Explanation
Entity Integrity No part of a primary key can be NULL.
Referential Integrity A foreign key must match an existing primary key value (or else
be NULL).
Column Integrity A column must contain only values consistent with the defined
data format of the column.
User-Defined Integrity The data stored in a database must comply with the rules of the
business.
All data integrity constraints should be enforced by the DBMS or the
application software.
Quick Note
• Data is inconsistent if multiple copies of an entry exist, and not all copies have been updated.
An inconsistent database can supply incorrect or contradictory information to its users.
Data Integrity - cont'd
The rules of a business can also determine the correct state for a database.
Such business rules are called User-Defined Data Integrity Constraints.
Example
A business has the following user-defined data integrity constraints.
An exempt employee is not paid for the tirst 5 hours of overtime worked.
An employee in the Finance Department cannot have a title of:
"Programmer".
A Salesman's commission cannot exceed 50% of salary.
Quick Notes
• User-defined data integrity constraints can be set by management policy or be required by
government laws.
• Frequently these business rules are completely arbitrary, or at least seem to be arbitrary.
• User-defined data integrity constraints may involve multiple columns and tables.
6
INITIAL DATABASE DESIGN
SECTION OBJECTIVES
At the end of this section, you will be able to:
1. Explain how Database Design fits into the Database Development Process.
2. Translate an entity-relationship data model into a relational database design.
3. Document a database design using Table Instance Charts.
DATABASE DESIGN
Database Design is performed during the Design Stage of the System
Development Cycle and is performed concurrently with Application Design.
Database Design - cont'd
Database Design is performed in two distinct activities.
Database Design Activities
1. Map the E-R Model to relational tables to produce an initial design.
2. Refine the initial design to produce a complete database design.
Database Design Deliverable
The Database Design Stage produces design specifications for a relational database including
definitions for relational tables, indexes, views, and storage space.
INITIAL DATABASE DESIGN OVERVIEW
Document each relational table on a Table Instance Chart.
Table Instance Chart
Table Name: EMPLOYEE
Column
Name
EMPNO FNAME LNAME JOB HIREDATE SAL COMM MGR DEPTNO
Key
Type
PK FK1 FK2
Nulls/
Unique
NN, U NN NN NN NN
7369 MARY SMITH CLERK 17-DEC-80 800 7902 20
7902 HENRY FORD ANALYST 03-DEC-81 3000 7566 50
7521 SUE WARD SALESMAN 22-FEB-81 1250 6000 7698 30
7698 BOB BLAKE MANAGER 01-MAY-81 2850 10000 7839 30
Sample
Data
7839 BOB KING PRESIDENT 17-NOV-81 5000 5000 10
Quick Notes
• The valid Key Types are PK for a Primary Key column, and FK for a Foreign Key column.
• Use suffixes to distinguish between multiple FK columns in a single table, for example, FK1
and FK2. Label multiple column keys with the same suffix.
• Use NN for a column that must be defined NOT NULL.
• Use U for a column that must be unique.
• If multiple columns must be unique in combination, label them with a suffix, for example U1.
• Label a single column PK as NN, U.
• Label a multiple column PK as NN, U1 or possibly as NN, U1 and U.
Initial Database Design Overview - cont'd
This familiar Training Company E-R Model will be used to illustrate the
activities of Initial Database Design.
Training Company E-R Model
Initial Database Design Overview - cont'd
Follow a set of steps to map an E-R Model to a set of relational tables
producing an initial database design.
Steps in Initial Database Design
1. Map the simple entities to tables.
2. Map attributes to columns and document sample data.
3. Map unique identifiers to primary keys.
4. Map relationships to foreign keys.
5. Choose arc options.
6. Choose subtype options.
MAP SIMPLE ENTITIES
Map each simple entity to a table. Create a Table Instance
Chart for the new table. Record only the name of the table.
Example
Create a Table Instance Chart for the INSTRUCTOR entity. Name the table
INSTRUCTOR.
Table Name: INSTRUCTOR
Column
Name
Key Type
Nulls/
Unique
Sample
Data
Quick Notes
• The table name should be easy to trace back to the entity name. The plural of the entity name
is sometimes used because the table will contain a set of rows.
• A simple entity is not a subtype or supertype. In Step 6, the designer must decide how to map
a supertype/subtype construct to tables.
MAP ATTRIBUTES TO COLUMNS
Map each attribute to a column in its entity's table. Map
mandatory attributes to NOT NULL (NN) columns.
Example
Map the attributes of the entity INSTRUCTOR to columns in the IN-
STRUCTOR table. Since id. first name. and last name are mandatory attributes,
designate their columns as NOT NULL.
Table Name: INSTRUCTOR
Column
Name
INST_ID FNAME LNAME PHONENO
Key Type
Nulls/
Unique
NN NN NN
Sample
Data
For each attribute, select a short but meaningful column name.
Quick Notes
• Column names should be easily traced o the E-R model.
• Avoid the use of SQL reserved words as column names - for example, NUMBER.
• Use consistent abbreviations to avoid programmer and user confusion. For example, will
Number be abbreviated as NO or NUM. Is it DEPTNO or DEPTNUM?
• Short column names will reduce the time required for SQL command parsing.
Map Attributes to Columns - cont'd
Document sample rows of data in each table's Table
Instance Chart.
Example
Document sample data for the columns of the INSTRUCTOR table.
Table Name: INSTRUCTOR
Column Name INST_ID FNAME LNAME PHONENO
Key
Type
Nulls/
Unique
NN NN NN
10 NANCY HALL 798-2251
81 MARIA GONZALES 756-4891
73 PETE CASSIDY 301-2291
95 KATHY ANDRONICA 483-9221
Sample Data
301 ERIC CAMPLIN 535-3166
Sources for Sample Data
• User interview notes
• Entity Instance Charts
• Current computer systems
• Other analysis stage documentation
• Additional conversations with the user
MAP UID'S TO PRIMARY KEYS
Map any attribute(s), which are part of the entity's UID to
PK column(s). Label the columns PK.
Example
The attribute id is the UID of the entity INSTRUCTOR, so make the
corresponding column INST_ID the PK of the INSTRUCTOR table.
Table Name: INSTRUCTOR
Column Name INST_ID FNAME LNAME PHONENO
Key Type PK
Nulls/ Unique NN, U NN NN
10 NANCY HALL 798-2251
81 MARIA GONZALES 756-4891
73 PETE CASSIDY 301-2291
95 KATHY ANDRONICA 483-9221
Sample Data
301 ERIC CAMPLIN 535-3166
A key type of PK indicates a primary key column.
Quick Notes
• All columns labeled PK must also be labeled NN and U.
• Map a UID, which includes multiple attributes to a composite PK. Label those columns NN
and U1
Map UID's to Primary Keys - cont'd
If an entity's UID includes a relationship, add foreign key
columns to the table and mark them as part of the primary
key.
Example
The UID of the ENROLLMENT entity is composed of its relationship to
COURSE and its relationship to STUDENT. Add two FK columns to the
ENROLLMENT table for the PK of the COURSE table and the PK of the
STUDENT table.
Quick Notes
• Choose a unique name for each FK column, and label the column(s) PK, NN, and FK.
• If multiple FK columns exist in a table, use suffixes to distinguish between them, for example,
FK1 and FK2. Label multiple column keys with the same suffix.
• Composite PK's must be unique in combination and should be labeled VI.
• Add sample data for the FK columns.
MAP RELATIONSHIPS TO FOREIGN KEYS
For M:1 relationships, take the PK at the one end and put
it in the table at the many end.
Example
Take the PK INST_ID at the one end, and put it in the table COURSE at the
many end.
Table Name: COURSE
Column Name COURSE_ CODE NAME FEE DUR INST_ID
Key Type PK FK
Nulls/ Unique NN, U NN
344 SQL*FORMS 1000 5 81
974 SQL*RW 400 2 73
401 DB DESIGN 400 2 95
717 DBA 900 3 73
Sample Data
659 SOL*PLUS 400 2 301
Go with the many!
Quick Notes
• Choose a unique name for the FK column, and label the column (s) FK.
• For must be relationships, label the column NN.
• Supply sample data.
Map Relationships to Foreign Keys - cont'd
If the table's PK includes a foreign key, the FK columns to
support the relationship may have been added in Step 3.
Example
The PK for the ENROLLMENT table included both the foreign key
COURSE_CODE and the foreign key ST_ID. Therefore, these two columns
already exist, and do not need to be added to support the relationships.
Map Relationships to Foreign Keys - cont'd
For a mandatory 1:1 relationship, place the unique FK in
the table at the mandatory end and use the NOT NULL
constraint to enforce the mandatory condition.
Example
Since the relationship from PERSONAL COMPUTER is mandatory, place the
FK for the relationship in the PERSONAL_COMPUTER table and label it NOT
NULL. MB_ID is the FK column added. The FK is labeled U to enforce the 1:1
relationship.
Table Name: PERSONAL COMPUTER Table Name: MOTHERBOARD
Column
Name
INV_NUM CASE_TYPE POWER_
SUPPLY
MB_ID
Key
Type
PK FK
Nulls/
Unique
NN, U NN NN NN, U
1045 BABY AT 150 4579
0437 BABY AT 200 8731
1458 TOWER 220 4773
1223 TOWER 220 9978
Sample
Data
1088 MINITOWER 200 4517
Column
Name
MB_ID PROC_
CHIP
PROC_
SPEED
COPROC_
CHIP
Key
Type
PK
Nulls/
Unique
NN, U NN NN NN
9978 486 33 N
4517 386 40 Y
4773 486 25 N
4579 386SX 25 N
Sample
Data
8731 386 33 Y
Map Relationships to Foreign Keys - cont'd
If a 1:1 relationship is optional in both directions, place the
FK in the table at either end of the relationship.
Example
For the optional 1:1 relationship between BERTH and SHIP, the FK column
could also be placed either in the BERTH or SHIP table. The B_NUM column is
added to the SHIP table, and labeled Unique to enforce the 1:1 relationship.
Map Relationships to Foreign Keys - cont'd
For a 1:M recursive relationship, add a FK column to the single table. This FK
column will refer to values of the PK column.
1.1.1. Example
For this 1:M recursive relationship, add an FK column to the EMPLOYEE table
for each employee's manager. Name the column MGR_ID to reflect the
relationship.
Table Name: EMPLOYEE
Column Name EMP_ID FNAME LNAME MGR_ID
Key Type PK FK
Nulls/ Unique NN, U NN NN
7450 MARY SMITH -
5579 LESLIE STERNE 7450
6714 JANET GENTRY 5579
9451 BILL ABLE 7450
Sample Data
3040 JUAN GOMEZ 9451
Quick Notes
• The FK column refers to a row in the same table.
• Name the FK column name to reflect the relationship.
• A recursive FK will never be NOT NULL.
Map Relationships to Foreign Keys - cont'd
For a 1:1 recursive relationship, add a unique FK to the
table. This FK column will refer to values of the PK
column.
Example
For this 1:1 recursive relationship, add a unique column to the PERSON table.
Table Name: PERSON
Column
Name
PERS_ID FNAME LNAME SPOUSE_ID
Key Type PK FK
Nulls/
Unique
NN, U1 NN NN U1
7450 MARY SMITH -
5379 SUSAN JONES 9451
6714 JANET GENTRY 3040
9451 BILL JONES 5579
Sample Data
3040 JERRY JOHNSON 6714
Quick Notes
• The combination of the PK and FK columns must always be unique in order to ensure the 1:1
relationship.
• A recursive FK will never be NOT NULL
• The additional constraint that a PERSON cannot be married to him/herself would have to be
implemented separately by the application programs or stored procedures.
REVIEW: MAPPING SIMPLE E-R MODELS TO TABLES
Map a simple Entity-Relationship model to an initial database design using
the following four steps:
Steps
1. Map simple entities to tables.
2. Map attributes to columns and document sample data.
3. Map UID's to Primary Keys.
4. Map relationships to Foreign Keys.
5. Document each table design on a Table Instance Chart.
EXERCISE 6-1
Create an initial database design.
1. Follow the first four steps of Initia l Database Design to map this E-R Model to a set of initial
table designs. Document your table designs on the supplied set of Table Instance Charts.
Create sample data as required.
Exercise 6-1 - cont'd
Table Name:
Column
Name
Key Type
Nulls/ Unique
Sample Data
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
EXERCISE 6-2
Create an initial database design.
1. Follow the first four steps of Initial Database Design to map this E-R Model to a set of initial
table designs. Document your table designs on the supplied set of Table Instance Charts.
Create sample data as required.
Exercise 6-2 - cont'd
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample
EXERCISE 6-3
Create an initial database design.
1. Follow the first four steps of Initial Database Design to map this E-R Model to a set of initial
table designs. Document your table designs on the supplied set of Table Instance Charts.
Create sample data as required.
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
Exercise 6-3 - cont'd
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample
EXERCISE 6-4
Optional Exercise
Create an initial database design.
1 Follow the first four steps of Initial Database Design to map this E-R Model to a set of initial
table designs. Document your table designs on the supplied Table Instance Charts. Use the
interview notes on the following page to select sample data for the Table Instance Charts.
Exercise 6-4 - cont'd
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
Table Name:
Column
Name
Key Type
Nulls/
Unique
Sample Data
Exercise 6-4 - cont'd
2 Use the following interview notes to select sample data for the Table Instance Charts.
"Our company sells products throughout the United States. So we've divided the U.S. into four
major sales regions: the Northern, Eastern, Southern, and Western Regions. Each sales region
has a unique region code. Each sales region is then divided into sales districts. For example, the
Western Region is divided into the Rocky Mountain, Northwest, Pacific Coast, and Pacific
Districts. Each district has a unique district code.
Each district is made up of sales territories. The Rocky Mountain District is composed of three
territories: Wyoming-Montana, Colorado, and Utah-New Mexico. The northwest District is
made up of two territories: The Washington and Oregon-Idaho territories. The Pacific Coast
District is composed of two territories: the California and Nevada territories. The Pacific
District includes the Hawaii territory and the Alaska territory. Each territory has a unique
territory code.
Then each sales territory is broken down into sales areas. For example, Colorado is made up of
two sales areas: the Front Range and the Western Slope sales areas. Each sales area has a unique
sales area code.
Each salesperson is responsible for one or more sales areas, and has a specific sales quota. We
also have sales managers who are responsible for one or more sales districts, and sales directors
who are responsible for one or more sales regions. Each sales manager is responsible for the
territories within his districts. We don't overlap our employees' responsibilities - a sales area is
always the responsibility of a single salesperson, and our managers and director's
responsibilities don't overlap. Sometimes our salespersons, managers, and directors will be on
leave or special assignments and will not have sales turf responsibilities. We identify all our
sales personnel by their employee ids."
MAP COMPLEX E-R MODELS TO TABLES
Follow the following additional steps to map a complex Entity-Relationship
Model to an initial database design.
Additional Steps
5 Choose Arc Options
6 Choose Subtype Options
CHOOSE ARC OPTIONS
Arcs represent a kind of multiple alternative foreign key.
Choose between two alternative designs for mapping arcs
to foreign keys.
Alternative Designs
• Explicit Arc Design
• Generic Arc Design
Example
This E-R Model will map to four tables. The OFFICE SUITE entity has an arc across the many ends
of three relationships, and corresponding FK columns must be added to the OFFICE_SUITE table.
Use either an Explicit Arc Design or a Generic Arc Design to add these multiple alternative foreign
keys.
Quick Notes
• Also use an Explicit Arc Design or a Generic Arc Design to implement multiple foreign keys
when an arc spans a set of 1:1 relationships.
• Arcs can only span relationship ends that are either all mandatory or all optional.
Choose Arc Options - cont'd
The Explicit Arc Design creates a foreign key column for
each relationship included in the arc.
Example
The following E-R Model contains four simple entities, and will be mapped to
four separate tables. The arc spans the many end of three relationships.
Therefore, FKs must be added to the OFFICE_SUITE table. Using an Explicit
Arc Design, create a FK column for each rela tionship.
Table Name: OFFICE_SUITE
Column Name BLDG_ ID SUITE_NUM INDIV_I
D
PARTNER_ CODE COMPANY_ NUMBER
Key Type PK PK FK1 FK2 FK3
Nulls/ Unique NN, U1 NN, U1
1024 101 30045
512 210 A4431
977 144 54532
3041 510 10844
Sample Data
2371 430 54101
Quick Notes
• The Explicit Arc Design will support multiple Foreign keys with different formats. For
example, INDIV_ID, PARTNER_CODE, and COMPANY_ID could all have a different
column format.
• Application software must enforce relationship exclusivity between the foreign keys.
Choose Arc Options - cont'd
The Generic Arc Design creates a single foreign key
column and one relationship flag column for the arc. Since
the relationships are exclusive, only one FK value will exist
for each row in the table.
Example
Again, create four separate tables for this E-R Model - one for each entity. Since
the arc spans the many end of the relationships, add the to the OFFICE_SUITE
table. Using the Generic Arc Design, create a single foreign key column, and
add a type column to indicate which of the three tables is referenced by the FK
column in each row. For example, J for INDIVIDUAL, P for PARTNERSHIP,
and C for COMPANY.
Table Name: OFFICE_SUITE
Column Name BLDG_ID SUITE_NUM RENTER _ID RENTER_ TYPE
Key Type PK PK FK
Nulls/ Unique NN, U1 NN, U1 NN NN
11124 1111 30045 1
512 2111 A4431 P
977 14 54532 1
MM 510 10844 C
Sample Data
2371 430 541111 C
Quick Notes
• If the relationships under the arc are mandatory, make both added columns NOT NULL.
• The foreign keys must share the same format for all referenced tables.
EXERCISE 6-5
Map arc structures to tables.
1 Using an Explicit Arc Design, develop a table design for this Entity-Relationship Model.
Document your design on the provided Table Instance Charts.
Table Name: STUDENT
Column Name
Key Type
Nulls/ Unique
Sample Data
Exercise 6-5 - cont'd
Table Name: COUNTY
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name: OTHER STATE
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name: FOREIGN COUNTRY
Column Name
Key Type
Nulls/ Unique
Sample Data
Exercise 6-5 - cont'd
2 Using a Generic Arc design, develop a table design for this Entity-Relationship Model.
Document your design on the provided Table Instance Charts.
Table Name: STUDENT
Column Name
Key Type
Nulls/ Unique
Sample Data
Exercise 6-5 - cont'd
Table Name: COUNTY
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name: OTHER STATE
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name: FOREIGN COUNTRY
Column Name
Key Type
Nulls/ Unique
Sample Data
CHOOSE SUBTYPE OPTIONS
Choose from three options for mapping subtypes to tables.
Subtype Table Mapping Options
• Single Table Design
• Separate Tables Design
• Arc Implementation (see Appendix E, p. E-4)
Example
In the following supertype/subtype construct, the EMPLOYEE, EXEMPT
EMPLOYEE, and NON-EXEMPT EMPLOYEE entities may be mapped to one,
two, or three tables, depending upon the subtype table mapping option selected.
Choose Subtype Options - cont'd
Option 1 - Single Table Subtype Design
Map the subtypes onto a single table for the supertype. The
single table will contain instances of all sub types.
Create
• single table for the supertype.
• a TYPE column to identify which subtype each row belongs to.
• a column for each of the supertype's attributes.
• a column for each of the subtype's attributes.
• FK columns for each of the supertype's relationships.
• FK columns for each of the subtype's relationships.
Use a single table design when the subtypes have few subtype-specific
attributes and relationships.
Choose Subtype Options - cont'd
Option 1 - Single Table Subtype Design
Example
Map the EMPLOYEE supertype and its subtypes onto a single EMPLOYEE
table.
Table Name: EMPLOYEE
Column Name BADGE_
NUM
FNAME LNAME EMP_ TYPE EE_
SALARY
NE_
HOURLY_
RATE
NE_
OVERTIME
_ RATE
NE_
UNION
_NUM
DEPT_ CODE
Key Type PK FK1 FK2
Nulls/ Unique NN, U NN NN NN NN
4579 JAMES JOYCE E 29000 40
6631 KAREN DIDONATO E 25000 35
1190 MICHAEL WEINTER E 42700 40
370 MARIA PENA E 44050 30
800 TERRY SMITH E 38450 35
7147 JOE SMITH NF 8.50 12.75 201 35
6794 JULIA WALKER NE 6.75 11.50 150 30
941 HARRY KAPLIN NE 12.00 18.00 201 45
1020 JOSE GOMEZ NE 9.50 16.15 201 30
Sample Data
3500 CLYDE JONES NE 10.50 15.75 180 45
Choose Subtype Options - cont'd
Option 1 - Single Table Subtype Design
The columns of the EMPLOYEE table are derived from the attributes and
relationships of the supertype and all its subtypes.
Entity
Type
Columns for
Attribtues
FK Columns for
Relationships
Supertype BADGE_NUM
FNAME LNAME
DEPT_CODE
Subtype EE_SALARY,
NE_HOURLY_RATE,
NE_OVERTIME_RATE
NE_UNION_NUM
Quick Note
• The single table subtype design requires that a new type column be created to identify each
row's subtype. The EMP_TYPE column was added to the EMPLOYEE table for this purpose.
Choose Subtype Options - cont'd
Option 1 - Single Table Subtype Design
Use the Single Table Subtype Design when there are few
subtype-specific attributes and relationships.
Design Advantages
• Access to the supertype is straightforward.
• The subtypes can be accessed and modified using views.
Design Disadvantages
• Subtype NOT NULL requirements cannot be enforced at the database level.
• Application logic will have to cater to different sets of attributes, depending on TYPE.
Choose Subtype Options - cont'd
Option 2 - Separate Tables Subtype Design
Map the subtypes onto separate tables - one for each
subtype. Each table will contain only instances of that
subtype.
Create
• a table for each subtype.
• a column for each attribute of a subtype in that subtype's table.
• a column for each attribute of the supertype in each of the subtype's table.
• an FK column for each relationship to a subtype in that subtype's table.
• an FK column for each relationship to the supertype in each of the subtype's tables.
Choose Subtype Options - cont'd
Option 2 - Separate Tables Subtype Design
Example
Map the EMPLOYEE supertype onto two tables - one for each subtype. First
create a separate table for the EXEMPT EMPLOYEE subtype.
Table Name: EXEMPT_EMPLOYEE
Column Name BADGE_NUM FNAME LNAME SALARY DEPT_CODE
Key Type PK FK
Nulls/ Unique NN, U NN NN NN NN
4579 JAMES JOYCE 29000 40
6631 KAREN DIDONATO 25000 35
1190 MICHAEL WEINER 42700 40
370 MARIA PENA 44050 30
Sample Data
800 TERRY SMITH 38450 35
Choose Subtype Options - cont'd
Option 2 - Separate Tables Subtype Design
Example - cont'd
Then create a separate table for the NON-EXEMPT EMPLOYEE subtype.
Table Name: NON_EXEMPT_EMPLOYEE
Column
Name
BADGE_
NUM
FNAME LNAME HOURLY_
RATE
OT_RATE UNION_
NUM
DEPT_ CODE
Key Type PK FK1 FK2
Nulls/
Unique
NN, U NN NN NN NN NN NN
7147 JOE SMITH 8.50 12.75 201 35
6794 JULIA WALKER 6.75 11.50 150 30
941 HARRY KAPLIN 12.00 18.00 201 45
1020 JOSE GOMEZ 9.50 16.15 201 30
Sample
Data
3500 CLYDE JONES 10.50 15.75 180 45
Choose Subtype Options - cont'd
Option 2 - Separate Tables Subtype Design
Use a Separate Tables Subtype Design when there are
many subtype-specific attributes or relationships.
Design Advantages
• The subtype's attribute optionality is enforced at the database level.
• Application logic does not require checks for subtypes.
Design Disadvantages
• Access to the supertype requires the UNION operator or a view with the UNION operator.
• Views that join the two tables are display only.
• Application program code must be specific to the individual subtype tables.
• Maintenance of UID's across subtypes is difficult to imple ment.
EXERCISE 6-6
Map subtypes to tables.
1 Using a Single Table Subtype Design, develop a table design for this Entity-Relationship
Model. Document your design on the supplied Table Instance Charts. Sample data is not
required.
Table Name: PRODUCT Table Name: ORDER
Exercise 6-6 - cont'd
Table Name: ORDER_LINE
Column
Name
Key Type
Nulls/
Unique
Sample
Data
Exercise 6-6 - cont'd
2 Using a Separate Tables Subtype Design, develop a table design for this Entity-Relationship
Model. Document your design on the supplied Table Instance Charts. Sample data is not
required.
Table Name: PRODUCT Table Name: ORDER
Exercise 6-6 - cont'd
Table Name: PRODUCT_ORDER_LINE
Column
Name
Key Type
Nulls/
Unique
Sample
Data
Table Name: SERVICE_ORDER_LINE
Column
Name
Key Type
Nulls/
Unique
Sample
Data
REVIEW: INITIAL DATABASE DESIGN
Map an Entity-Relationship Model to an initial database design using the
following interrelated steps.
Steps for Mapping Entity-Relationship Models
1 Map simple entities to tables.
2 Map attributes to columns and document sample data.
3 Map UID's to Primary Keys.
4 Map relationships to Foreign Keys.
5 Choose arc options.
6 Choose subtype options.
Document an initial database design on Table Instance Charts.
7
TABLE NORMALIZATION
SECTION OBJECTIVES
At the end of this section, you will be able to:
1 Define normalization and explain its benefits.
2 Place tables in Third Normal Form.
3 Explain how conceptual data modelling rules ensure normalized tables.
NORMALIZE TABLES
Categorize tables according to their degree of normalization.
Normal Form Rule Description
First Normal Form (1NF) The table must be expressed as a set of unordered, two-
dimensional tables. The table cannot contain repeating
groups.
Second Normal Form (2NF) The table must be in INF. Every non-key column must be
dependent on all parts of the primary key.
Third Normal Form (3NF) The table must be 2NF. No non-key column may be
functionally dependent on another non-key column.
"Each non-primary key value MUST be dependent on the key, the whole
key, and nothing but the key."
Why normalize tables?
• Normalization minimizes data redundancy. Unnormalized data is redundant.
• Data redundancy causes integrity problems. Update and delete transactions may not be
consistently applied to all copies of the data causing inconsistencies in the data.
• Normalization helps identify missing entities, relationships, and tables.
Quick Notes
• Third normal form is the generally accepted goal for a database design that eliminates
redundancy.
• Higher normal forms are not widely used.
RECOGNIZE UNNORMALIZED DATA
Unnormalized data does not comply with any of the rules of normalization.
Example
Consider the following set of data. Three variable length records are shown - one for each
ORDER_ID. Why is this data unnormalized?
ORDER
ID
DATE CUSTOMER
ID
CUSTOMER
NAME
STATE ITEM
NUM
ITEM
DESCRIP
QUANTITY PRIC
E
2301 6/23 101 Volleyrite IL 3786
4011
9132
net
racket
3-pack
3
6
8
35.00
65.00
4.75
2302 6/25 107 Herman's WI 5794 6-pack 4 5.00
2303 6/26 110 We-R-Sports MI 4011
3141
racket
cover
2
2
65.00
10.00
It contains a repeating group of ITEM NUM, ITEM DESCRIPTION, QUANTITY, and PRICE. First Normal Form prohibits repeating groups.
CONVERT TO FIRST NORMAL FORM
Remove any repeating groups.
Steps
1 Remove the repeating group from the base table.
2 Create a new table with the PK of the base table and the repeating group.
Example
Convert the following set of unnormalized data to First Normal Form.
ORDER ID
DATE CUSTOMER ID
CUSTOMER NAME
STATE ITEM NUM
ITEM DESCRIP
QUANTITY PRICE
2301 6/23 101 Volleyrite 1L 3786 4011 9132
net racket 3-pack
3 6 8
35.00 65.00 4.75
2302 6/25 107 Herman's Wl 5794 6-pack 4 5.00
2303 6/26 110 We-R-Sports MI 4011 3141
racket cover
2 2
65.00 10.00
Remove the repeating group of ITEM NUM, ITEM DESCRIPTION, QUA NTITY, and PRICE. The PK of the remaining table is ORDER ID. Create a new ORDERJTEM table with ORDER ID and the repeating group.
ORDER
ORDER ID DATE CUSTOMER ID CUSTOMER NAME STATE PK 2301 6/23 101 Volleyrite IL 2302 6/25 107 Herman's WI 2303 6/26 110 We-R-Sports MI ORDER ITEM
ORDER ID ITEM NUM ITEM DESCRIP QUANTITY PRICE PK,FK PK 2301 2301 2301 2302 2303 2303
3786 4011 9132 5794 4011 3141
Net racket 3-pack 6-pack racket cover
3 6 8 4 2 2
35.00 65.00 4.75 5.00 65.00 10.00
CONVERT TO SECOND NORMAL FORM
Remove any non-key columns that are not dependent upon the table's
entire primary key.
Steps
1 Determine which non-key columns are not dependent upon the table's entire primary key.
2 Remove those columns from the base table.
3 Create a second table with those columns and the column(s) from the PK that they are
dependent upon.
Example
Put the following table in2NF.
ORDER
ORDER ID DATE CUSTOMER ID CUSTOMER NAME STATE
PK
2301
2302
2303
6/23
6/25
6/26
101
107
110
Volleyrite
Herman's
We-R-Sports
IL
WI
MI
The ORDER table is already in 2NF. Any value of ORDERJD uniquely determines a single value of each column. Therefore, all columns are dependent on the PK ORDERJD.
Quick Notes
• If each column is not dependent upon the entire primary key, the table is not in 2NF.
• Any table with a single column primary key is automatically in 2NF.
Convert to Second Normal Form - cont'd
Remove any non-key columns that are not dependent upon the table's
entire primary key.
Example
Put the following table in 2NF.
ORDER ITEM
ORDER ID ITEM
NUM
ITEM
DESCRIP
QUANTITY PRICE
PK,FK PK
2301
2301
2301
2302
2303
2303
3786
4011
9132
5794
4011
3141
Net
racket
3-pack
6-pack
racket
cover
3
6
8
4
2
2
35.00
65.00
4.75
5.00
65.00
10.00
The ORDERJTEM table is not in 2NF since PRICE and DESCRIPTION are dependent upon ITEM NUM, but not dependent upon ORDER ID. To convert the table to 2NF, remove any partially dependent columns. Create an ITEM table with those columns and the column from the PK that they are dependent upon.
ORDER ITEM ITEM
ORDER ID ITEM NUM QUANTITY
PK.FK PK.FK
2301
2301
2301
2302
2303
2303
3786
4011
9132
5794
4011
3141
3
6
8
4
2
2
ITEM NUM DESCRIPTION PRICE
PK
3786 net 35.00
4011 racket 65.00
9132 3-pack 4.75
5794 6-pack 5.00
3141 cover 10.00
CONVERT TO THIRD NORMAL FORM
Remove any columns that are dependent upon another non-key column.
Steps
1 Determine which columns are dependent upon another non-key column.2
2 Remove those columns from the base table.
3 Create a second table with those columns and the non-key column that they are dependent
upon.
Example
Put the ORDER table in Third Normal Form.
ORDER
ORDER ID DATE CUSTOMER ID CUSTOMER NAME STATE
PK
2301
2302
2303
6/23
6/25
6/26
101
107
110
Volleyrite
Herman's
We-R-Sports
IL
WI
MI
CUSTOMER NAME and STATE are dependent upon CUSTOMER ID. CUSTOMER ID is not the PK. Therefore, the ORDER table is not in 3NF. Move the dependent non-key columns with the non-key column they depend upon Into a new CUSTOMER table.
ORDER CUSTOMER
ORDER ID DATE CUSTOMER ID
PK FK
2301 6/23 101
2302 6/25 107
2303 6/26 110
CUSTOMER ID CUSTOMER
NAME
STATE
PK
101 Volleyrite IL
107 Herman's WI
110 We-R-Sports MI
Quick Note
• A table is in Third Normal Form if no non-key column is functionally dependent upon another
non-key column.
Convert to Third Normal Form - cont'd
No non-key column can be functionally dependent upon another non-key
column.
Example
Consider the ORDER JTEM table. Is it in 3NF? Why or why not?
ORDER ITEM
ORDER
ID
ITEM
NUM
QUANTITY
PK,FK PK.FK
2301
2301
2301
2302
2303
2303
3786
4011
9132
5794
4011
3141
3
6
8
4
2
2
All non-key attributes are dependent on the key, the whole key, and nothing but the key. The
ORDERJTEM table is in 3NF.
Example
Consider the ITEM table. Is it in 3NF? Why or why not? ITEM
ITEM DESCRIPTION PRICE
NUM
PK
3786 net 35.00
4011 racket 65.00
9132 3-pack 4.75
5794 6-pack 5.00
3141 cover 10.00
All non-key attributes are dependent on the key, the whole key, and nothing but the key. The ITEM
table is in 3NF.
EXERCISE 7-1
Normalize a set of data.
1. Put the following data into First, Second, and Third Normal Form on the supplied Table
Instance Charts. Three variable length records are shown-one for each EMP_NUM.
EMPLOYEE
First Normal Form
Table Name: Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name: Column Name
Key Type
Nulls/ Unique
Sample Data
Exercise 7-1 - cont'd
Second Normal Form
Table Name:
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name:
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name:
Column Name
Key Type
Nulls/ Unique
Sample Data
Exercise 7-1 - cont'd
Third Normal Form
Table Name:
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name:
Column Name
Key Type
Nulls/ Unique
Sample Data
Table Name:
Column Name
Key Type
Nulls/ Unique
Sample Data
Exercise 7-1 - cont'd
Third Normal Form - cont'd
Table Name:
Column Name
Key Type
Nulls/ Unique
Sample Data
NORMALIZE DURING DATA MODELLING
Ensure a 3NF table design by following the rules of data modelling.
First Normal Form Rule
• A table must contain no repeating groups.
Corresponding Data Modelling Rule
• All attributes must be single -valued.
Example
Is the entity CLIENT in 1NF? If not, how could it be converted to 1NF?
The attribute date contacted has multiple values, therefore the entity CLIENT is not in 1NF. Create an
additional entity CONTACT with a M:1 relationship to CLIENT. Create an additional entity and 1 :M
relationship to ensure 1 NF.
Normalize During Data Modelling - cont'd
Validate each attribute's dependence upon its entity's entire UID.
Second Normal Form Rule
• Every non-key column must be dependent upon all parts of the primary key.
Corresponding Data Modelling Rule
• An attribute must be dependent upon its entity's entire unique identifier.
Example
Are all of the attributes in the following E-R diagram dependent upon their entity's UID?
The attribute bank location is not dependent upon the UID of ACCOUNT. It is dependent upon the UID of BANK. Move the attribute and place it where it depends upon the UID of it's entity.
Normalize During Data Modelling - cont'd
Verify attribute placement to ensure a normalized table design.
Third Normal Form Rule
• No non-key column can be functionally dependent upon another non-key column.
Corresponding Data Modelling Rule
• No non-UID attribute can be dependent upon another non-UID attribute.
Example
Are any of the non-UID attributes for this entity dependent upon another non-UID attribute?
The attributes customer name and state are dependent upon the customer id. Create another entity called CUSTOMER with a UID of customer id, and place the attributes accordingly.
8
FURTHER DATABASE DESIGN
SECTION OBJECTIVES
At the end of this section, you will be able to:
1. Specify referential integrity constraints.
2. Design indexes.
3. Understand database views.
4. Evaluate table denormalization.
5. Work with your DBA to plan physical storage usage.
FURTHER DATABASE DESIGN
Review the default table design against the application module's
requirements, and refine and extend the initial design to produce a
complete database design.
Activities
• Define referential integrity constraints.
• Design indexes.
• Establish views.
• Denormalize the database design.
• Plan physical storage usage.
SPECIFY REFERENTIAL INTEGRITY
A foreign key column value must match an existing primary key column
value (or else be NULL). Use referential integrity constraints to specify how
referential integrity is to be maintained.
Delete Constraint
• What happens if a row containing a referenced primary key is deleted?
Update Constraint
• What happens if a referenced primary'key is updated? *
* Only an issue if the PK is updateable in the first place.
Specify Referential Integrity - cont'd
Specify a Delete Constraint to define what should happen if a row
containing a referenced primary key is deleted.
Options: CASCADE, RESTRICTED, or NULLIFY (only if NULLs are
allowed)
Example
Consider the EMPLOYEE and DEPARTMENT tables. What should happen if a DEPT.NO for which
employees work is deleted from the DEPARTMENT table?
Table Name: EMPLOYEE Table Name: DEPARTMENT
Option Explanation of Constraint
CASCADE The deletion should cascade to the matching employees. The matching EMPLOYEE rows should also be deleted.
RESTRICTED The deletion should be restricted to only DEPARTMENTS without employees.
NULLIFY The foreign key should be nullified (valid only for FK's allowing NULLs) when the referenced PK is deleted.
Specify Referential Integrity - cont'd
Specify an Update Constraint to define what should happen when a
referenced primary key is updated. (The Update Rule is only meaningful if
the PK is updateable.)
Options: CASCADE, RESTRICTED, or NULLIFY (only ifNULLs are
allowed)
Example
What should happen if a DEPT_NO for which employees work is changed to another
DEPT_NO?
Table Name: EMPLOYEE Table Name: DEPARTMENT
Option Explanation of Constraint
CASCADE The update should cascade to the matching employees. The matching
EMPLOYEE rows should also be updated to reflect the new PK value.
RESTRICTED The update should be restricted to only DEPARTMENTS without employees.
NULLIFY The foreign key should be nullified (valid only for FK's allowing NULLs) when the referenced PK is updated to a new PK value.
DESIGN INDEXES
An index is associated with a single physical table and contains the values of
one or more columns from that table.
Database Design - Table Instance Chart
Table Name: COURSE
Physical Representations
COURSE Table
I_COURSES_PRIME Index
(Unique)
I_COURSES_2 Index
(Not Unique)
Design Indexes - cont'd
Use indexes to significantly improve data access time.
Indexes
• Provide quick access to rows of data and avoid full table scans
• Facilitate table joins
• Ensure uniqueness of a value if defined as unique
• Are used automatically when. referenced in the WHERE clause of a SQL statement if the
column is not modified
For further information on the subject see:
SQL Language Reference Manual. 778-V6.0
ORACLE RDBMS Database Administrator's Guide Version 6.0,3601-V6.0
Design Indexes - cont'd
A concatenated index is an index created on a group of columns in a single
table. Map a composite key to a concatenated index.
Example
The ENROLLMENT table has a composite PK of COURSE_CODE and ST_ID. Create a composite
key called I_ENROLL_PRIME on both columns.
Table Name: ENROLLMENT Table Design
Column Name
ENROLL_ DATE
DATE_ COMPLETEC
GRADE COURSE_ CODE
STJD
Key Type
PK.FK1 PK.FK2
Nulls/ Unique
NN NN.U1 NN.U1
20-JUL-91 19-AUG-91 -- 344 47592 05-SEP-91 - -- 401 15402 14-JUN-91 28-JUL-91 A 717 51394 08-MAY-9 28-JUL-91 B 717 94572
Sample Data
05-MAY-9 21-MAY-91 A 401 51394
ENROLLMENT Table Physical Tables
ROW ID
ENROLL_ DATE
DATE_ COMPLETED
GRADE COURSE_ CODE
ST_ID
5011 20-JUL-91 19-AUG-91 - 344 47592 5012 05-SEP-91 - - 401 15402 5015 14-J UN-91 28-JUL-91 A 717 51394 5013 08-MAY-91 28-JUL-91 B 717 94572 5014 05-MAY-91 21-MAY-91 A 401 51394
I_ENROLL_PRIME Index (Unique)
COURSE_ CODE
ST_ID ROW ID
344 47592 5011 401 15402 5012 401 51394 5014 717 51394 5015
717 94572 5013
Design Indexes - cont'd
Use indexes to implement keys and to support application access
requirements.
Build Indexes for
• Primary keys (unique indexes)
• Foreign keys (generally non-unique indexes)
Consider indexing
• Alternate keys (unique indexes)
• Any critical non-key columns used in WHERE clauses
• Any search keys
Indexes add storage and update overhead.
Quick Notes
• A unique index references a column or set of columns that has unique values in the table.
• A non-unique index references a column or set of columns that are not unique in a table.
• Be aware that under certain conditions, indexes are not used by the RDBMS.
For further information on the subject see:
ORACLE RDBMS Database Administrator's Guide Version 6.0,3601-V6.0
ORACLE RDBMS Performance Tuning Manual 5317-V6.0
ESTABLISH VIEWS
Establish database views to meet application access requirements
Views can be used for:
• restricting access.
• providing referential integrity.
• presenting tables to users in any form.
• pre-packaging complex queries.
• producing rapid prototypes.
• pre-joined base tables in SQL*Forms.
• checking data input.
A view can be thought of as a predefined window onto the database.
Quick Notes
• A view has no data of its own and merely relays information from underlying tables.
• A view is defined by a SELECT statement that is named and stored in the ORACLE Data
Dictionary.
• A view is queried as if it were a table.
Establish Views - cont'd
A View can restrict what the user, designer, or tool sees.
Examples
A View of the EMP table could be used to restrict users from seeing the employees' salaries.
A view can be used to present normalized data in a denormalized form.
Example
Following the rules of normalization, the ORDER and CUSTOMER tables are separate.
A view defined across both tables could be used to pre-join the tables so the user would only see a
single table.
Establish Views - cont'd
Use views with caution. Access through a view is slower because it requires
an extra access to the data dictionary, and may cause query optimization to
be slower.
View Limitations
• For a view based upon a single table, the SQL INSERT, UPDATE, and DELETE commands
have no limitations.
• For multi-table views with virtual columns, INSERT, UPDATE, and DELETE are restricted.
• When accessing tables through a view, it is possible to add rows not visible through the view
unless the WITH CHECK OPTION is specified.
DENORMALIZE THE DATABASE DESIGN
Always start with tables in Third Normal Form.
Beware of Denormalization!
• Be extremely reluctant to denormalize the default table design.
• Denormalization can cause data inconsistency problems.
Denormalization may be a solution for transactions with performance
requirements such as:
• high throughput.
• high frequency.
• quick response time.
Consider all other options prior to denormalization, especially adding or
changing the index structure.
Denormalize the Database Design - cont'd
Combining tables is the most common form of denormalization.
Example
Consider the ACCOUNT and BANK tables.
If high-volume account queries always access the bank name, a combined table might be worth the data redundancy. The ACCOUNT table and the BANK table are combined on BANK_NUM.
Denormalize the Database Design - cont'd
Individual codes tables may be combined into a reference table for
validating and decoding coded values for an entire application system.
Example
The following separate codes tables are required for an application system. They are used to provide
the SQL*Forms list of values feature and to validate table values for INSERT or UP DATE.
Combine all the tables into a single table with an additional column, CODE_TYPE, that defines which set of values the code belongs to. Create a view for each CODE_TYPE.
Denormalize the Database Design - cont'd
Establish a companion CODE_TYPE table for validating code description
lengths.
Example
The CHAR_CODE table on the previous page includes four different types of codes. Each of these
code types has a different valid length for its code description. Set up a CODE_TYPE table for
validating the length of the descriptions.
The table contains two columns, CODE_TYPE and LENGTH. LENGTH is the maximum description length for each CODE_TYPE.
Denormalize the Database Design - cont'd
A vector is a one-dimensional array with a fixed number of values - a
repeating group of definite size. Represent vector data as either a set of
rows or a set of columns.
Column-Wise Table Design (3NF)
Row-Wise Table Design
Denormalize the Database Design - cont'd
Choose the table design for vector data based upon the functional access
requirements.
Advantages of a Column-Wise Design
• SQL group functions act on columns, e.g., SUM, AVG.
• Changes in the vector length can be easily accommodated.
Advantages of a Row -Wise Design
• On the input form, all data values can appear on a single line.
• All values can be inserted with a single INSERT statement.
• The storage space requirement is lower.
• Output reports showing all values horizontally are easy to produce.
Denormalize the Database Design - cont'd
Reconsider storing derived data in light of the functional access
requirements and the capabilities of the software development tools.
Example
A regional sales manager has 200 salespersons working for him. He frequently queries the total sales
quota and sales-to-date for his region. The sales quotas are established quarterly. Sales data is updated
weekly. Maintaining sales quota data by region would be desirable, and maintaining sales-to-date
might also be desirable.
PLAN PHYSICAL STORAGE USAGE
Work with the Database Administrator to plan the physical placement of
the database tables and indexes.
Considerations
• For each table and index, estimate the amount of disk space required.
• Decide on the placement of tables and indexes on logically separate tablespaces and
physically separate disks.
• Define storage allocation parameters based upon the expected patterns of data update and
growth.
For further information on the subject see:
ORACLE RDBMS Database Administrator's Guide Version 6.0,3601-V6.0
SUMMARY: DATABASE DESIGN
Database Design is the process of mapping the information requirements
reflected in an Entity-Relationship Model into a relational database.
Activity 1: Initial Database Design
• Map the simple entities to tables.
• Map attributes to columns and document sample data.
• Map unique identifiers to primary keys.
• Map relationships to foreign keys.
• Choose arc options.
• Choose subtype options.
Activity 2: Further Database Design
• Define referential integrity constraints.
• Design indexes.
• Establish views.
• Denormalize the database design.
• Add system support tables.
• Plan physical storage usage.
SUMMARY: DATABASE DEVELOPMENT
This course has covered the first two steps of the top-down database
development process. The last step is Database Build.
DATABASE BUILD OVERVIEW
In Database Build, create physical relational database tables to implement
the database design.
Example
The following Structured Query Language (SQL) statements will create the DEPARTMENT and
EMPLOYEE tables.
SQL> 2 3 4
CREATE TABLE DEPARTMENT DEPTNO NUMBER (2) NOT NULL PRIMARY KEY, DNAME CHAR(20) NOT NULL, LOC CHAR (15) NOT NULL ) ;
SQL> 2 3 4 5 6 7 8 9
10
CREATE TABLE EMPLOYEE EMPNO NUMBER (5) NOT NULL PRIMARY KEY, FNAME CHAR (15) NOT NULL, LNAME CHAR(15) NOT NULL, JOB CHAR(9), HIREDATE DATE NOT NULL, SAL NUMBER(7,2), COMM NUMBER(7,2), MGR CHAR(4) REFERENCES EMPLOYEE(EMPNO),
DEPTNO NUMBER(2) NOT NULL REFERENCES DEPARTMENT (DEPTNO) );
For further information on the subject attend:
Introduction to ORACLE for Developers