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Mapping Constraints

A database must conform to certain defined constraints of the contents.

 

Mapping Cardinalities

Mapping cardinalities is the number of entities to which another entity can be linked through a relationship set. 

There are four types of mapping cardinalities.

 

Let  A and B be two entity sets.

 

  1. a) One-to-one : An entity in A is associated with no more than one entity in B and an entity in B is associated with no more than one entity in A.

 

  1. b) One-to-many : An entity in A is associated with many entities in B and an entity in B is associated with at most one entity in A.

 

  1. c) Many-to-one : Many entities in A can be associated with at most one entity in B and an entity in B can be associated with many entities in A.

 

  1. d) Many-to-many : Many entities in A can be associated with many entities in B and many entities in B can be associated with many entities in A.

Participation Constraints :

  1. a) Total :  The participation of an entity set E in a relationship R is considered ‘total’ if every entity in E participates in R.

 

  1. b) Partial : If only some entities in E participate in relationship R, then it is called ‘partial’.

 

Reference:

Mapping Constraints of Database.