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§2 – The Relational Model and

Normalization

Fen Wang

wangfen@cwu.edu

Lecture 4

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Chapter Objectives

• The foundation of the relational model

• Characteristics of relations

• The basic relational terminology

• Primary, candidate, and composite keys

• The purpose and use of surrogate keys

• How foreign keys represent relationships

• The meaning of functional dependencies

• Possible insertion, deletion, and update anomalies

• Apply a process for normalizing relations

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The Relational Database Model

• The dominant database model is the relational database model – all current major DBMS products are based on it

• Created by IBM engineer E. F. Codd in 1970

• It was based on mathematics called relational algebra

• Now the standard model for commercial DBMS products

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Important Relational Model Terms

• Entity • Relation • Functional Dependency • Determinant • Candidate Key • Composite Key • Primary Key • Surrogate Key • Foreign Key • Referential integrity constraint • Normal Form • Multivalued Dependency

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Entity

• An entity is something of importance to a user that needs to be represented in a database:

– Customers

– Computers

– Sales

• An entity represents one theme or topic

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Relation

• Relational DBMS products store data about entities in relations, a special type of table

• A relation is a two-dimensional table that has specific characteristics

• The table dimensions, like a matrix, consist of rows and columns

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Characteristics of a Relation

Smart tip: if a table qualifies to be a relation, it must satisfy all of the

above characteristics!

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A Sample Relation

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A Relation with Values of Varying Length

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Tables That Are Not Relations

Cells of the table hold multiple values

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Tables That Are Not Relations

Cells of the table require a particular row order/arrangement

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Tables That Are Not Relations

EmployeeNumber Phone LastName

100 335-6421 Abernathy

101 215-7789 Cadley

104 610-9850 Copley

100 335-6421 Abernathy

107 299-9090 Jackson

No two rows may be identical

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Alternative Terminology

• Although not all tables are relations, the terms table and relation are often used interchangeably

• The following sets of terms are equivalent:

Line format to indicate a table structure

• In addition to using graphic format to display or show a table structure, you could also utilize a line format (a.k.a. textual format) to indicate a table structure:

RELATION_NAME (Column01, Column02, … LastColumn)

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Keys

• A key is a combination of one or more columns that is used to identify rows in a relation

• A composite key is a key that consists of two or more columns

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Uniqueness of Keys

Unique Key Nonunique Key

Data value is unique for each row.

Consequently, the key will uniquely identify a row.

Data value may be shared among several rows.

Consequently, the key will identify a set of rows.

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Uniqueness of Keys (cont.)

• See below for a sample table using the line format:

TEXTBOOK (Author, Title, ISBN, Publisher, Copyright)

– Analyze each column in the table

• Is it a unique or non-unique key?

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Sample answers:

Possible unique keys: ISBN

Possible non-unique keys: Author,

Title, Publisher, Copyright

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A Candidate Key

• A candidate key are keys that uniquely identify each row in a relation

• A candidate key is a unique key

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Primary Keys

• A primary key is a candidate key selected as the primary means of identifying rows in a relation:

– There is one and only one primary key per relation

– The primary key may be a composite key

– The ideal primary key is short, numeric and never changes

EMPLOYEE(EmployeeNum,FirstName,LastName,Department,Email,Phone)

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Primary Keys Example

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Composite Primary Key Example

• To identify a grade, you need to know a StudentID, CourseID, and Session (e.g., Fall 2009)

• The composite key is:

(StudentID, CourseID, Session)

• One needs to know the value of all three columns to uniquely identify a grade

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A Surrogate Key

• A surrogate key is a unique, numeric value that is added to a relation to serve as the primary key

• Surrogate key values have no meaning to users and are usually hidden on forms, queries and reports

• A surrogate key is often used in place of a composite primary key

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Surrogate Key Example

NOTE: The primary key of the relation is underlined below:

• RENTAL_PROPERTY without surrogate key:

RENTAL_PROPERTY (Street, City, State/Province, Zip/PostalCode, Country, Rental_Rate)

• RENTAL_PROPERTY with surrogate key: RENTAL_PROPERTY (PropertyID, Street, City,

State/Province, Zip/PostalCode, Country, Rental_Rate)

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Defining the Primary Key in Microsoft Access

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Defining the Primary Key in Microsoft SQL Server

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Defining the Primary Key in MySQL

Check the PK

checkbox to

indicate the

Primary Key

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Defining the Primary Key in Oracle

Make drop-down

box selection to

indicate the

Primary Key

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Before next class

• Practice more with MS Access 2010 and MS Visio Professional

• Keep working on Project D1

• Start working on Assignment#2 (due 10PM on Friday)

• Read Textbook Chapter 1 – The Access WorkBench Section 1