; Department of Computer Science, University of Pittsburgh, Pittsburgh, PA 15260.; Department of Electrical Engineering and Computer Science, University of Illinois at Chicago, Chicago, IL 60680.
A database management system can ensure the semantic integrity of a database via an integrity control subsystem. A technique for implementation of such a subsystem is proposed. After a database is updated by transactions, its integrity must be verified by evaluation of a set of semantic integrity assertions. For evaluation of an integrity assertion a number of database pages need to be transferred from the secondary storage to the fast memory. Since certain pages may be required for evaluation of different integrity assertions, the order of the evaluation of the integrity assertions determines the total number of pages fetched from the secondary storage. Hence, the schedule for the evaluation determines the cost of the database verification process. We show that the search for an optimal schedule is an NP-hard problem. Four approximation algorithms that find suboptimal schedules are proposed. They are based on the utilization of intersections among sets of pages required for the evaluation of different integrity assertions. The theoretical worst case behaviors of these algorithms are studied. Finally, the algorithms are compared via a simulation study to a naive, random order verification approach. The methods proposed for minimizing the costs of the batch integrity verification also apply to other problems that can be abstracted to the directed traveling salesman optimization problem. For example, the methods are applicable to multiple to multiple-query optimization and to concurrency control via the predicate locks.
Department of Computer Science, University of Pittsburgh, Pittsburgh, PA 15260.; Department of Electrical Engineering and Computer Science, University of Illinois at Chicago, Chicago, IL 60680.