Although less prevalent than functional dependency, join dependency and multivalued dependency can guide the design of the database. But inclusion dependency is widespread. It is a statement in which a few of the columns of a relation are in the other columns. Typically, inclusion dependency has a very insignificant influence on the design of a database. For example, a foreign key is inclusion dependency.
Explanation of inclusion dependency
Let there be the relations S and R that was acquired by the translation of entity sets so that every S entity is an R entity.
- Inclusion dependency occurs when the relation obtained by the projection of S on the key attributes is the same as that retrieved from R. There should be no splitting up of the collections of attributes that take part in the inclusion dependency.
- Generally, the inclusion dependencies are based on keys.
