SQL Server Notification Services Question:

Data Integrity
Data Integrity validates the data before getting stored in the columns of the table.
SQL Server supports four type of data integrity:
Entity Integrity

Entity Integrity can be enforced through indexes, UNIQUE constraints and PRIMARY KEY constraints.

Domain Integrity
Domain integrity validates data for a column of the table.
It can be enforced using:

Foreign key constraints,
Check constraints,
Default definitions
NOT NULL.
Referential Integrity

FOREIGN KEY and CHECK constraints are used to enforce Referential Integrity.
User-Defined Integrity

It enables you to create business logic which is not possible to develop using system constraints. You can use stored procedure, trigger and functions to create user-defined integrity.