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Integrity Rules in Relational Database Model

Integrity rule 1: Entity integrity

It says that no component of a primary key may be null.

All entities must be distinguishable. That is, they must have a unique identification of some kind. Primary keys perform unique identification function in a relational database. An identifier that was wholly null would be a contradiction in terms. It would be like there was some entity that did not have any unique identification. That is, it was not distinguishable from other entities. If two entities are not distinguishable from each other, then by definition there are not two entities but only one.

Integrity rule 2: Referential integrity

The referential integrity constraint is specified between two relations and is used to maintain the consistency among tuples of the two relations.

Suppose we wish to ensure that value that appears in one relation for a given set of attributes also appears for a certain set of attributes in another. This is referential integrity.

The referential integrity constraint states that, a tuple in one relation that refers to another relation must refer to the existing tuple in that relation. This means that the referential integrity is a constraint specified on more than one relation. This ensures that the consistency is maintained across the relations.

Table A
DeptID DeptName DeptManager
F-1001 Financial Nathan
S-2012 Software Martin
H-0001 HR Jason

Table B
EmpNo DeptID EmpName
1001 F-1001 Tommy
1002 S-2012 Will
1003 H-0001 Jonathan

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