Inclusion Dependency

• Multivalued dependency and join dependency can be used to guide database design although they both are less common than functional dependencies.
• Inclusion dependencies are quite common. They typically show little influence on designing of the database.
• The inclusion dependency is a statement in which some columns of a relation are contained in other columns.
• The example of inclusion dependency is a foreign key. In one relation, the referring relation is contained in the primary key column(s) of the referenced relation.
• Suppose we have two relations R and S which was obtained by translating two entity sets such that every R entity is also an S entity.
• Inclusion dependency would be happen if projecting R on its key attributes yields a relation that is contained in the relation obtained by projecting S on its key attributes.
• In inclusion dependency, we should not split groups of attributes that participate in an inclusion dependency.
• In practice, most inclusion dependencies are key-based that is involved only keys.