1. The Relational Model UC Berkeley Extension pmcdermott@msn.com Copyright © 2008 Patrick McDermott

2. History

3. Tables A “Relation” is a Table –NOT so called because of ERD Relationships A Set of named Columns An Arbitrary number of unnamed Rows Each Row is identified by a unique Key

4. Relational Database Systems  Data is represented in a collection of two- dimensional tables.  Relationships between the data in the tables are expressed by values tables.  Using SQL, you can create relationships between the data in a dynamic fashion on the fly.  The relationships between the data entities do not necessarily need to be defined or envisioned when the database is first created.

5. Relational Model Components 1.Data Structure DDL: Data Definition Language 2.Data Manipulation DML: Data Manipulation Language 3.Data Integrity Business Rules re Key Referents

6. Data Definition Language CREATE TABLE ALTER TABLE DROP TABLE CREATE INDEX CREATE VIEW Defines the Database

7. Properties of Relational Tables 1.Entries in columns are single-valued 2.Entries in columns share the same domain 3.Each Row is Unique 4.The Sequence of columns has no significance 5.The Sequence of rows has no significance 6.Each column has a unique name

8. Characteristics of a Relation 1.Rows contain data about an entity 2.Columns contain data about attributes of the entity 3.Cells of the table hold a single value 4.All entries in a column are of the same kind 5.Each column has a unique name 6.The order of the columns is unimportant 7.The order of the rows is unimportant 8.No two rows may be identical