§2 – The Relational Model and Normalization Fen Wang [email protected] Lecture 4 IT468 DB @ ITAM 1 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 IT468 DB @ ITAM 2 1 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 IT468 DB @ ITAM 3 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 IT468 DB @ ITAM 4 2 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 IT468 DB @ ITAM 5 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 IT468 DB @ ITAM 6 3 Characteristics of a Relation Smart tip: if a table qualifies to be a relation, it must satisfy all of the above characteristics! IT468 DB @ ITAM 7 A Sample Relation IT468 DB @ ITAM 8 4 A Relation with Values of Varying Length IT468 DB @ ITAM 9 Tables That Are Not Relations Cells of the table hold multiple values IT468 DB @ ITAM 10 5 Tables That Are Not Relations Cells of the table require a particular row order/arrangement IT468 DB @ ITAM 11 Tables That Are Not Relations No two rows may be identical EmployeeNumber Phone LastName 100 335-6421 Abernathy 101 215-7789 Cadley 104 610-9850 Copley 100 335-6421 Abernathy 107 299-9090 Jackson IT468 DB @ ITAM 12 6 Alternative Terminology • Although not all tables are relations, the terms table and relation are often used interchangeably • The following sets of terms are equivalent: 13 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) IT468 DB @ ITAM 14 7 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 IT468 DB @ ITAM 15 Uniqueness of Keys Unique Key Nonunique Key Data value is unique Data value may be for each row. shared among several Consequently, the key rows. will uniquely identify Consequently, the key a row. will identify a set of rows. 16 8 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? Copyright Publisher, Title, Author, Author, unique - non keys: keys: Possible ISBN unique keys: keys: Possible answers: Sample IT468 DB @ ITAM 17 A Candidate Key • A candidate key are keys that uniquely identify each row in a relation • A candidate key is a unique key IT468 DB @ ITAM 18 9 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) 19 Primary Keys Example IT468 DB @ ITAM 20 10 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 IT468 DB @ ITAM 21 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 IT468 DB @ ITAM 22 11 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) IT468 DB @ ITAM 23 Defining the Primary Key in Microsoft Access IT468 DB @ ITAM 24 12 Defining the Primary Key in Microsoft SQL Server IT468 DB @ ITAM 25 Defining the Primary Key in MySQL Check the PK checkbox to indicate the Primary Key IT468 DB @ ITAM 26 13 Defining the Primary Key in Oracle Make drop-down box selection to indicate the Primary Key IT468 DB @ ITAM 27 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 IT468 DB @ ITAM 28 14 .