Referential Integrity in the E-R Model

1. These constraints arise frequently. Every relation arising from a relationship set has referential integrity constraints.

     
   Figure 5.1: An n-ary relationship set
   

   • Figure 5.1 shows an n-ary relationship set relating entity sets .
   • Let denote the primary key of .
   • The attributes of the relation scheme for relationship set include .
   • Each in the scheme for is a foreign key that leads to a referential integrity constraint.
2. Relation schemes for weak entity sets must include the primary key of the strong entity set on which they are existence dependent. This is a foreign key, which leads to another referential integrity constraint.