Justi cation for Inclusion Dependency Normal Form

Functional dependencies (FDs) and inclusion dependencies (INDs) are the most fundamental integrity constraints that arise in practice in relational databases. In this paper we address the issue of normalisation in the presence of FDs and INDs and in particular the semantic justiication for Inclusion Dependency Normal Form (IDNF), a normal form which combines Boyce-Codd normal form with the restriction on the INDs that they be noncircular and key-based. We motivate and formalise three goals of database design in the presence of FDs and INDs: non interaction between FDs and INDs, elimination of redundancy and update anomalies , and preservation of entity integrity. We show that, as for FDs, in the presence of INDs being free of redundancy is equivalent to being free of update anomalies. Then, for each of these properties we derive equivalent syntactic conditions on the database design. Individually, each of these syntactic conditions is weaker than IDNF and the restriction that an FD not be embedded in the right hand-side of an IND is common to three of the conditions. However, we also show that for these three goals of database design to be satissed simultaneously IDNF is both a necessary and suucient condition.