ON THE SEMANTICS OF UPDATES IN DATABASES.

A methodology is suggested for updating databases with integrity constraints and rules for deriving inexplicit information. First considered is the problem of updating arbitrary theories by inserting into them or deleting from them arbitrary sentences. The solution involves two key ideas: when replacing an old theory by a new one to minimize the change in the theory, and when there are several theories that involve minimal changes, one looks for a new theory that reflects that ambiguity. The methodology is also adapted to updating databases, where different facts can carry different priorities, and to updating user views. Refs.