Relationship Sets keys:

As primary key of an entity set allow us to distinguish among the various entities of the set. So we also need a similar mechanism to distinguish among the various relationships of a relationship set. Let R be a 'Relationship set' involving entities sets E1, E2, E3,...En let primary key(Ei) denote the set of attributes that forms the set of attributes that forms the primary key for entity set (Ei).

***Assume the attributes name of all primary keys are unique, and each entity set participates only once in the relationship. ***

Then the composition of the primary key for a relationship That depends on the set of attributes associated with the relationship set R.

Relationship Here since is an attribute of relationship majorIn.

Like' john majors in "Cs" since 2000.

If relationship set R has no attribute associated with it, then the set of attributes. Individual relationship Individual relationship_set

If the relation set R has attributes(a1,a2,a3, Associated with it. Then the set of attributes

Primary key(E1)U Primary key(E2)U......Primary key(En)U{a1,a2,a3,} describes an individual relationship in set R.Relationship_no-attribute

Facebook Likes