The Relational Model

UC Berkeley Extensionpmcdermott@msn.com

Copyright © 2008 Patrick McDermott

History

Codd Relational Model 1970

Codd 3NF 1972

Boyce/Codd 1974

Fagin 4NF 1977

Fagin 5NF 1979

TablesA “Relation” is a Table

– NOT so called because of ERD RelationshipsA Set of named ColumnsAn Arbitrary number of unnamed RowsEach Row is identified by a unique Key

Relational Database SystemsData 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.

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

Data Definition Language

CREATE TABLEALTER TABLEDROP TABLE

CREATE INDEXCREATE VIEW

Defines the

Database

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

Characteristics of a Relation 1. Rows contain data about an entity 2. Columns contain data about attributes of

the entity3. Cells of the table hold a single value 4. All entries in a column are of the same

kind5. Each column has a unique name 6. The order of the columns is unimportant7. The order of the rows is unimportant 8. No two rows may be identical