Foundations of Canonical Update Support for Closed Database Views

A closed view of a database schema is one which is totally encapsulated. Insofar as the user is concerned, the view is the database schema. The rest of the database system is not visible through the view, and is is not required for complete use of the view. Similarly, the updates which may be effected through the view have their scope limited entirely to that view. In this paper, we lay the mathematical foundations for the systematic support of such views. The proper context is shown to be that of update translation under constant meet complement, a refinement of the constant complement strategy of Bancilhon and Spyratos. The central complexity result for relational schemata is that checking the legality of updates is “infinitely” simpler than blindly checking that the new state is legal for the view schema, and in the particular case that the base schema is constrained by functional dependencies, may always be performed in constant time, even if the view schema is not finitely axiomatizable. We further establish that, under very natural assumptions, update strategies for closed views are unique. This paper appeared in the Proceedings of the Third International Conference on Database Theory (ICDT90), Paris, 12–14 December 1990, Springer-Verlag Lecture Notes in Computer Science, Volume 470, pp. 422–436. †The research reported herein was performed while the author was visiting the Department of Mathematics of the University of Oslo, Norway. He wishes to thank in particular the members of the Computational Linguistics Group for their kind hospitality during his stay there.