Relational Database Concepts

The Relational Model

Developed by Edgar F. Codd in 1970, the relational model organizes data into tables (relations) with rows and columns.

Key Components

Tables (Relations)

• Collection of related data entries
• Consists of rows and columns
• Each table represents an entity

Rows (Tuples/Records)

• Individual data entries in a table
• Each row represents a single instance of an entity

Columns (Attributes/Fields)

• Properties or characteristics of an entity
• Define the structure of data in a table

Domains

• Set of allowable values for an attribute
• Defines data type and constraints

Primary Keys

• Uniquely identifies each row in a table
• Cannot contain NULL values
• Cannot have duplicate values
• Can be composite (multiple columns)

Foreign Keys

• Column(s) that reference primary key of another table
• Establishes relationships between tables
• Maintains referential integrity

Relational Integrity Rules

Entity Integrity

• Primary key cannot be NULL
• Primary key must be unique

Referential Integrity

• Foreign key values must match existing primary key values
• Or foreign key can be NULL (if allowed)

Domain Integrity

• Values must be within defined domain
• Data type constraints must be followed

Relationships

One-to-One (1:1)

• Each record in Table A relates to one record in Table B

One-to-Many (1:M)

• Each record in Table A can relate to multiple records in Table B

Many-to-Many (M:N)

• Records in both tables can relate to multiple records in the other
• Requires junction table to implement