11-1 © Prentice Hall, 2004 Chapter 11: Physical Database Design Object-Oriented Systems Analysis and Design Joey F. George, Dinesh Batra, Joseph S. Valacich, Jeffrey A. Hoffer

Chapter © Prentice Hall, 2004 Chapter Objectives Af ter 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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Chapter © Prentice Hall, 2004 What Is Physical Database 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

Chapter © Prentice Hall, 2004 Sometimes, the analyst and the designer are the same person, Deliverables

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Chapter © Prentice Hall, 2004 What Is SQL? Structured Query Language The standard language for creating and using relational databases ANSI Standards – SQL-92 – most commonly available – SQL-99 – included object-relational features

Chapter © Prentice Hall, 2004 Common 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

Chapter © Prentice Hall, 2004 Example CREATE TABLE Statements Here, a table called DEPT is created, with one numeric and two text fields. The numeric field is the primary key.

Chapter © Prentice Hall, 2004 SELECT The SELECT, and FROM clauses are required. All others are optional. WHERE is used very commonly.

Chapter © Prentice Hall, 2004 Example SELECT Statements Select * from EMP where ENAME = ‘SMITH’; Select EMPNO, ENAME From EMP where JOB = ‘SALESMAN’ order by ENAME;

Chapter © Prentice Hall, 2004 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 Select EMPNO, ENAME, DNAME from EMP, DEPT where EMP.DEPT_NO = DEPT.DEPT_NO;

Chapter © Prentice Hall, 2004 Example Data Manipulation Commands Insert into DEPT values (50, ‘DESIGN’, ‘MIAMI’); Update EMP set SAL = 3000 where EMPNO = 7698; Delete from EMP where EMPNO = 7844

Chapter © Prentice Hall, 2004 Designing Fields Field – 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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Chapter © Prentice Hall, 2004 Mapping a composite attribute onto multiple fields with various data types

Chapter © Prentice Hall, 2004 Creating and Using Composite Attribute Types

Chapter © Prentice Hall, 2004 Data 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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Chapter © Prentice Hall, 2004 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

Chapter © Prentice Hall, 2004 This will result in null values in several rows’ application data.

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Chapter © Prentice Hall, 2004 This will result in duplications of item descriptions in several rows of the CanSupplyDR table.

Chapter © Prentice Hall, 2004 Duplicate regionManager data

Chapter © Prentice Hall, 2004 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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Chapter © Prentice Hall, 2004 Determining Table Scan Time A table scan is a complete read of the file block by block, regardless of the number of row objects in the answer to a query Block – a unit of data retrieval from secondary storage Blocking factor – the number of row objects that fit in one block

Chapter © Prentice Hall, 2004 Determining Table Scan Time (Continued) 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

Chapter © Prentice Hall, 2004 What Is a Heap? A file with no organization Requires full table scan for data retrieval Only use this for small, cacheable tables

Chapter © Prentice Hall, 2004 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

Chapter © Prentice Hall, 2004 What Is an Indexed File 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

Chapter © Prentice Hall, 2004 Random 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.

Chapter © Prentice Hall, 2004 Issues to Consider When Selecting a File Organization File size Frequency of data retrievals Frequency of updates Factors related to primary and foreign keys Factors related to non-key attributes

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Chapter © Prentice Hall, 2004 Recap Af ter studying this chapter we learned to: – Design database fields. – Evaluate denormalization situations. – Design file organization structures. – Design object-relational features.