Working with Keys
A primary key is a constraint that assures that each table contains no duplicate rows. A foreign key is a constraint that enforces referential integrity. For more information about keys, see Keys.
For details about working with keys, see the following topics.
How to: Modify Foreign Key Relationships
How to: Delete Foreign Key Relationships
How to: View Foreign Key Properties
How to: Disable Foreign Key Constraints for Replication
How to: Disable Foreign Key Constraints with INSERT and UPDATE Statements
Reference (Visual Database Tools)