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Topic 9:Topic 9:Physical Database DesignPhysical Database Design

Object-Oriented Systems Analysis and Design

Joey F. George, Dinesh Batra,

Joseph S. Valacich, Jeffrey A. Hoffer

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Chapter ObjectivesChapter Objectives

After studying this chapter you should be able to:– Design database fields.– Evaluate denormalization situations.– Design file organization structures.– Design object-relational features.

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What Is Physical Database What Is Physical Database Design?Design?

The part of a database design that deals with efficiency considerations for access of data

Processing speed, storage space, and data manipulation are key issues in physical database design

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Sometimes, the analyst and the designer are the same person,

Deliverables

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What Is SQL?What Is SQL?

Structured Query Language

Often pronounced “sequel”

The standard language for creating and using relational databases

ANSI Standards– SQL-92 – most commonly available– SQL-99 – included object-relational features

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Common SQL CommandsCommon SQL Commands

CREATE TABLE – used to define table structures and link tables together

SELECT – used to retrieve data using specified formats and selection criteria

INSERT – used to add new rows to a table

UPDATE – used to modify data in existing table rows

DELETE – used to remove rows from tables

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Example CREATE TABLE Example CREATE TABLE StatementStatement

Here, a table called DEPT is created, with one numeric and two text fields.

The numeric field is the primary key.

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Example INSERT StatementExample INSERT Statement This statement inserts a new row into the DEPT

table

DEPTNO’s value is 50 DNAME’s value is “DESIGN” LOC’s value is “MIAMI”

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SELECTSELECTThe SELECT, and FROM clauses are required.

All others are optional.

WHERE is used very commonly.

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SELECT Statement: Example 1SELECT Statement: Example 1

Select * from DEPT;

Result: all fields of all rows in the DEPT table

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SELECT Statement: Example 2SELECT Statement: Example 2

Select * from EMP where ENAME = ‘SMITH’;

Result: all fields for employee “Smith”

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SELECT Statement: Example 3SELECT Statement: Example 3

Select EMPNO, ENAME From EMP where JOB = ‘SALESMAN’ order by ENAME;

Result: employee number, name and job for only salesmen from the EMP table, sorted by name

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What Is a Join Query?What Is a Join Query?

A query in which the WHERE clause includes a match of primary key and foreign key values between tables that share a relationship

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SELECT Statement: Example 4SELECT Statement: Example 4

Select EMPNO, ENAME, DNAME from EMP, DEPT where EMP.DEPT_NO = DEPT.DEPT_NO and DEPT.LOC = ‘CHICAGO’;

Result: all employees’ number and name (from the EMP table, and their associated department names, obtained by joining the tables based on DEPT_NO.

Only employees housed in department located in Chicago will be included

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SELECT Statement: Example 4SELECT Statement: Example 4(cont.)(cont.)

Join queries almost always involve matching the primary key of the dominant table with the foreign key of the dependent table.

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What Is an Aggregation Query?What Is an Aggregation Query?

A query results in summary information about a group of records, such as sums, counts, or averages

These involve aggregate functions in the SELECT clause (SUM, AVG, COUNT)

Aggregations can be filtered using the HAVING clause and/or grouped using the GROUP BY clause

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SELECT Statement: Example 5SELECT Statement: Example 5

Select JOB, Avg(SALARY) from EMP Group by JOB Having Avg(SALARY) >= 3000;

The job name and average salary for each job of employees in the EMP table.

Only jobs with average salaries exceeding $3000 will be included

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SELECT Statement: Example 5SELECT Statement: Example 5(cont.)(cont.)

Note that clerks and salesmen are not included, because the average salaries for these jobs are below $3000.

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Example Data ManipulationExample Data Manipulation

Update EMP set SAL = 3000 where EMPNO = 7698;– Modifies the existing employee’s (7698) salary

Delete from EMP where EMPNO = 7844– Removes employee 7844 from the EMP table

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Designing FieldsDesigning FieldsField – the smallest unit of named application data

recognized by system software such as a DBMS

Fields map roughly onto attributes in conceptual data models

Field design involves consideration of identity, data types, sizes, and constraints

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Data type –A coding scheme recognized by system software for representing organizational data

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Considerations for Choosing Considerations for Choosing Data TypesData Types

Balance these four objectives:

1. Minimize storage space

2. Represent all possible values of the field

3. Improve data integrity for the field

4. Support all data manipulations desired for the field

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Mapping a composite attribute onto multiple fields with various data types

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Creating and Using Composite Creating and Using Composite Attribute TypesAttribute Types

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Data Integrity ControlsData Integrity Controls

Default Values – used if no explicit value is entered

Format Controls – restricts data entry values in specific character positions

Range Controls – forces values to be among an acceptable set of values

Referential Integrity – forces foreign keys to align with primary keys

Null Value Controls – determines whether fields can be empty of value

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Referential integrity is important for ensuring that data relationships are accurate and consistent

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What Is Denormalization?What Is Denormalization?The process of combining normalized

relations into physical tables based on affinity of use of rows and fields, and on retrieval and update frequencies on the tables

Results in better speed of access, but reduces data integrity and increases data redundancy

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This will result in null values in several rows’ application data.

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This will result in duplications of item descriptions in several rows of the CanSupplyDR table.

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Duplicate regionManager data

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What Is a File Organization?What Is a File Organization?

A technique for physically arranging the row objects of a file

Main purpose of file organization is to optimize speed of data access and modification

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Secondary Storage ConceptsSecondary Storage Concepts

Block – a unit of data retrieval from secondary storage

Extent – a set of contiguous blocksScan – a complete read of a file block by

blockBlocking factor – the number of row objects

that fit in one block

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Determining Table Scan TimeDetermining Table Scan Time

Block read time is determined by seek, rotation and transfer.

Average table scan time equals #rows in table divided by blocking factor multiplied by block read time

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What Is a Heap?What Is a Heap?

A file with no organization

Requires full table scan for data retrieval

Only use this for small, cacheable tables

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What Is Hashing?What Is Hashing?A technique that uses an algorithm to

convert a key value to a row address

Useful for random access, but not for sequential access

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What Is an Indexed File What Is an Indexed File Organization?Organization?

A storage structure involving indexes, which are key values and pointers to row addresses

Indexed file organizations are structured to enable fast random and sequential access

Index files are fast for queries, but require additional overhead for inserts, deletes, and updates

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Random Access Processing Using B+ Tree IndexesRandom Access Processing Using B+ Tree Indexes

Indexes are usually implemented as B+ trees

These are balanced trees, which preserve a sequential ascending order of items as they are added.

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Issues to Consider When Issues to Consider When Selecting a File OrganizationSelecting a File Organization

File sizeFrequency of data retrievalsFrequency of updatesFactors related to primary and foreign keysFactors related to non-key attributes

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Which Fields should be Indexed?Which Fields should be Indexed?

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Design of Object Relational Design of Object Relational FeaturesFeatures

Object-relatonal databases support:– Generalization and inheritance– Aggregation– Mulivalued attributes– Object identifiers– Relationships by reference (pointers)

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Generalization in Oracle 9i/10gGeneralization in Oracle 9i/10g

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Aggregation in Oracle 9i/10gAggregation in Oracle 9i/10g

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Multivalued Attributes in Oracle 9i/10gMultivalued Attributes in Oracle 9i/10g

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Object Identifiers in Oracle 9i/10gObject Identifiers in Oracle 9i/10g

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RecapRecap

After studying this chapter we learned to:– Design database fields.– Evaluate denormalization situations.– Design file organization structures.– Design object-relational features.