Relational Data Model: The Foundation of Modern Databases

Explore the fundamental concepts of the relational data model, which underpins most modern database systems. Learn about tables, tuples, relation instances, schemas, keys, and attributes. Understand the importance of relational integrity constraints in ensuring data validity and consistency.

DBMS - Relational Data Model

The Relational Data Model is the most widely used data model worldwide for data storage and processing. Known for its simplicity, it encompasses all the necessary properties and functionalities to ensure efficient data storage and processing.

Key Concepts

  • Tables − In the relational model, data is stored in tables, which represent the relationships between entities. Each table has rows (records) and columns (attributes).
  • Tuple − A single row within a table is referred to as a tuple and contains one complete record of that relation.
  • Relation Instance − A finite collection of tuples within a relational database forms a relation instance, where duplicate tuples are not allowed.
  • Relation Schema − This defines the structure of a relation by specifying the table name, its attributes, and their respective names.
  • Relation Key − One or more attributes that uniquely identify each row within a table are known as the relation key.
  • Attribute Domain − Every attribute has a specified range of permissible values, known as its domain.

Relational Integrity Constraints

To ensure validity, every relation must satisfy specific conditions known as Relational Integrity Constraints. The main types of integrity constraints include:

1. Key Constraints

A relation must have at least one minimal subset of attributes that can uniquely identify a tuple, known as a key. If there are multiple such minimal subsets, they are called candidate keys. Key constraints ensure:

  • No two tuples in a relation with a key attribute can have identical values for key attributes.
  • Key attributes cannot contain NULL values.

These are also known as Entity Constraints.

2. Domain Constraints

Each attribute has a specific range of acceptable values, mirroring real-world scenarios. For instance, an attribute like age must be a positive integer, as negative age values are unrealistic. Domain constraints help to enforce these realistic boundaries on attribute values.

3. Referential Integrity Constraints

Referential integrity constraints utilize foreign keys, which are key attributes of one relation that reference key attributes of another (or the same) relation. This constraint mandates that a key element being referred to in a relation must actually exist in the referenced relation.