In: Computer Science
Describe "Disjointness Constraints" and provide an example business rule involving an overlap rule.
DISJOINT CONSTRAINTS:
It is the relationship between members of the subclasses and indicates whether it is possible for a member of superclass to be a member of one,or more than one,subclass.
It applies only when a super class has more than one subclass.If the subclasses are disjoint,then an entitiy occurances can be a member of only one of thesubclasses.eg,postgradsor undergrads.
If the value of a descriminator is not null and appears in supertype entity instance then that must be linked with theonly one subtype.This is called disjoint constraint.
business rule involving an overlap rule.
In overlapping constraint,the supertype entity instance can appear in many subtype instances.
In overlapping example consider a teacher can be a student also.then 't' can be linked with student and teacher subtype entity.
suppose Member is super class and its sub-classes one is student and another one is faculty.if(Member)of subclass(student or faculty)not both then it is disjoint.if member both of its subclass then it non-disjoint or overlapping