Correctness of semantic integrity checking in database management systems

Altough today's applications are very demanding with regard to semantic integrity, few real database systems provide capabilities of this type. in this paper, a definition of integrity constraint is given in terms of the Relational Algebra. Then certain aspects are discussed concerning transactions management in the presence of integrity constraints. In particular, the problem of when to enforce a set of Integrity constraints during the execution of a transaction is addressed. To this purpose the notion of Integrity Enforcement Schedule is introduced. An Integrity Enforcement Schedule represents the sequence of integrity checking actions performed during the execution of a transaction. A correctness criterion for the Integrilty Enforcement Schedules is established, and a condition is presented which is sufficient to ensure the correctness. Finally the notion of Minimal Integrity Enforcement Schedule is introduced. The Minimal Integrity Enforcement Schedules are those Integrity Enforcement Schedules in which every constraint is verified "as soon as possible". For this reason they are really desirable in the transaction management to avoid expensive rollbacking operations. Algorithms for their construction are presented, together with the associated correctness proofs.