1

Database Design

Sections 4 & 5Subtype, Supertype, Mutually exclusive, non-transferability, transferable, 1:1, 1:M, M:M, Redundant, Intersection entity, Barred relationship, CRUD analysis

2

DJs on Demand – Partial ERD

3

Reserved Words

A reserved work is one that has a specific meaning and function in the computer system, language, or database.

Examples: NULL DATE DISTINCT

4

Video Store – example next slide

Identify business rules Construct ERD Class activity

5

Video Store example

Read the given business scenario and walk through the steps below.

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 the entity.

6. Diagram each entity and a few of its attributes.  Remember, entity names are always singular.

7. Identify the relationships and draw them on the ERD.

6

Video ERD

featured in

•TAPE/DVDnumberformat

MOVIEid

titlecategory

ACTORstage namereal name

CUSTOMERmembership

numberlast namefirst name

phone number

a copy of

on

the feature ofrented by

the renter of

7

Use Source Documents

Source document assist in identifying entities, attributes, and relationships

8

Subtype

A subtype: inherits all attributes of the supertype inherits all relationships of the supertype usually has its own attributes or

relationships is drawn within the supertype never exists alone may have subtypes of its own is also known as a "subentity“

9

Subtype & Supertype

Supertype (entity) can be subdivided into Subtypes

Example:

JOBmanager

clerksales

support

10

Attributes

Supertype can have attributes at supertype level

Attributes at supertype level are for all subtypes

Subtypes can have own attributes for only that attribute

11

Example

EXAM#number

*description*weight*date

*grade for written component

MIDTERM*grade for

oral presentation

FINAL*extra pts for opt. paper

QUIZ

BONUS QUESTIONS

STUDENT

included in

include

taken by

takes

12

Global Fast Food Employees STAFF is an entity with supertypes What are the attributes of STAFF?

#id *first name *last name *DOB *salary

What subtypes exist in STAFF? ORDER TAKER *overtime COOK *training OTHER

Are there any attributes in any of the subtypes?

13

Example: an incorrect subtypes in the illustration.

AUTOMOBILE subtypes are not mutually exclusive

AUTOMOBILE possible solution

BUILDING subtypes have problem of not being exhaustive, should be minimum of 2 types

14

Subtype Needs Exhaustive:

Every instance of the supertype is also an instance of one of the subtypes.

Treating all parts or aspects without omissions. 2 or more items

Mutually exclusive: Every instance of the supertype is of one and

only one subtype. A relationship that presents choices which are

unable to be true at the same time.

15

Correctly identify subtypes

When considering supertypes and subtypes, you can use three questions to see if the subtype is correctly identified:1. Is this subtype a kind of supertype?2. Have I covered all possible cases?

(exhaustive)3. Does the example fit into one and only

one subtype? (mutually exclusive)

16

Nested subtypes

17

Documenting Business Rules

Source documents assist in identiying: entities attributes relationships Some business rules are “implemented

by programming”

18

Business Rules Recognize if Business rule is implemented

by the data model or by programming Example:

Only an employee with a title of manager can manage other employees

The event planner must contact the customer before the DJ can be assigned

Business rules can be changed as society changes or business leaders feel change is needed

19

Business rule types Structural

Must be entered at time of initial data entry Example: When ORDER entered a staff id must

be entered Does not require code written to enforce

Procedural Work flow related Programmed validation is procedural constraint

Generally need to write code Example: Commission can not be > 25% of

salary

20

Structural Business Rule examples:

21

Procedural Business Rule example:

22

Discussion Students must have studied algebra and

geometry in order to sign up for trigonometry. Could you represent this in the ERD?

• How would you implement this with programming?

• If the student had taken the subjects, can you think of an additional business rule that a school may want in this scenario?

23

Each entity has

Name Optionality Cardinality Transferability

Example on next slide.

24

Relationship Transferability

25

Relationship transferability Rules established for the purpose such as

safety, efficiency, or increased profit Example: Airline tickets

can be transferable or non-transferable?

Non-transferable means also not updatable symbol used to denote non-

transferable blood type is non-transferable

26

Non-transferable relationship

Orders are non-transferable Resolution would be to cancel order

and create new order

CUSTOMER ORDER

place

placed by

27

Example 5.1 exercise 1 a

Each town may be the birthplace of many people. Each person must be born in one and only one town.

PERSON TOWNbirthplace for

born in

28

Relationship types

One to One (1:1) One to Many (1:M) Many to Many (M:M)

29

One to One relationship

30

One to One relationship

Usually few of these relationships Often mandatory at one side If mandatory at both ends be aware,

it might be a error. Possible should be only one entity not two

PERSON BYCYCLE

ride

ridden by

31

One to One relationship

32

One to Many relationship

33

One to Many

Most common type are mandatory on one side and optional on the other

Mandatory at both ends models entities that cannot exist without each other

ORDERORDER TYPE

34

One to Many example

TAX RETURNTAX REPORT

LINE

BAND MUSICIANcomposed of

belong to

composed of

entered in

35

Many to Many relationship

36

Many to Many

Often common in initial version of ERD

Later stage of design converted to other type

STUDENT TEACHERlearn from

educate

37

Redundant relationship

Redundant relationship is one that can be derived from another relationship in the model

38

Many to Many Relationship Resolution

All M:M relationships must be changed to a set of 1:M and M:1 relationship

Insert a transition entity between Occurs when you go from conceptual

model to design model

39

Example: M:M with Intersection Entity

STUDENT COURSE

REGISTRATION

40

Resolving M:M with Intersection

Create an intersection entity If you can’t find a good intersection

entity create one by concatenate two entities together

41

Example

PARTNER EVENT

WORK ASSIGNMENT (PARTNER_EVENT)

42

CRUD analysis

Create ER models that reflect all business rules gathered during the interview process Identify the create, retrieve, update, and

delete (CRUD) requirements of the business

Validate your ER model by performing a CRUD analysis

43

CRUD requirements CRUD analysis will help you:

Translate between the consultant and the client. Provide a guideline for the DBA who will

eventually build the database. Check that you haven’t missed any entities or

relationships in your data model. Check to make sure that you haven’t modeled

anything that the business does not require.

44

What is CRUD?

CRUD is an acronym for create, retrieve, update, delete.

Check for completeness and accuracy.

45

Create keywords

Look for these words when you interview the client.

INPUT ENTER LOAD IMPORT RECORD CREATE

46

Retrieve keywords Look for: VIEW REPORT BRING UP PRINT FIND READ LOOK UP

47

Update keywords

Look for: CHANGE MODIFY ALTER UPDATE

48

Delete keywords

Look for: DISCARD REMOVE TRASH PURGE DELETE

49

CRUD analysis

If you have a business function that has no entity to CRUD against, then your data model may be incomplete. Similarly, if you have entities in your ERD that are not touched by any CRUD (there is no business function that creates, retrieves, updates, or deletes from it), then you may not need that entity in your model.