Integrity

Integrity constraints are used to ensure accuracy and consistency of data in a relational database.[citation needed] Data integrity is handled in a relational database through the concept of referential integrity. There are many types of integrity constraints that play a role in referential integrity.

Types

Codd, initially defined two sets of constraints, but in his second version of the relational model, he came up with five integrity constraints[citation needed]:

Entity integrity

The entity integrity constraint states that no primary key value can be null. This is because the primary key value is used to identify individual tuples in a relation . Having null value for the primary key implies that we cannot identify some tuples.

Referential Integrity

The referential integrity constraint is specified between two relation and is used to maintain the consistency among tuples in the two relations. Informally, the referential integrity constraint states that a tuple in one relation that refers to another relation must refer to an existing tuple in that relation.

Domain Integrity

Column Integrity

User Defined Integrity

In software engineering, an entity-relationship model (ERM) is an abstract and conceptual representation of data. Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created by this process are called entity-relationship diagrams, ER diagrams, or ERDs.

The definitive reference for entity-relationship modeling is Peter Chen's 1976 paper.[1] However, variants of the idea existed previously,[2] and have been devised subsequently.

Overview

The first stage of information system design uses these models during the requirements analysis to describe information needs or the type of information that is to be stored in a database. The data modeling technique...