Constraint In ER Model:
There are two types of constraint in ER model
Mapping Cardinalities
Participation Constraints
Mapping Cardinalities or Cardinality Ratios:
It tells the number of entities to with another entity can be associated through a 'relationship set' . Mapping cardinality uses binary relationship sets.
So a binary relationship set R between entity set A and B there will be one of this mapping cardinality.One to One Mapping Cardinality
An entity in A is associated with " at most " One entity in B and an entity in B is associated with at most one entity in A.
One to Many Mapping Cardinality
An entity in A is associated with any number(Zero more) of entities B. An entity in B, however, can be associated with at most one entity in A
Many to One Mapping Cardinality
An entity in A is associated with at most one entity in B. An entity in B, however can be associated with any number (zero or more) of entities in A.
Many to Many Mapping Cardinality
:An entity in A is associated with any number(zero or more) of entities in B, and an entity in B is associated with any number (zero or more) of entities in A.
Participation Constraints:
The participation of an entity set E in a relationship set R is said to be ' total' if every entity in E participate in at least one relationship in R. If only some entities in E participate in relationship in R, then entity set E in relationship R is said to be partial.
