SCDBR: A Reasoner for Specifications in the Situation Calculus of Database Updates

In 2], Reiter presents a formalism for database updates speciication. He uses the \situation calculus", that is, many-sorted rst-order languages for representing knowledge about dynamically changing worlds that evolve through diierent states when actions are executed. In these worlds, properties of their objects depend on the current state of the world. These properties are called uents and correspond in our context to database tables. The speciication of a dinamically changing world, like a database, typically contains the following information: (1) state independent knowledge about the objects of the world, (2) knowledge about the state of the world at the initial situation S 0 , (3) preconditions for performing the diierent actions; a binary predicate Poss is introduced to say that the execution of an action is possible at a state, (4) the immediate eeects of actions, when they are possible, in terms of the uents whose truth values are known to be changed by the execution of the action. The knowledge contained in items (1) and (2) is called the inital database D 0. EXAMPLE: Let us consider a library database. For reasons of space we outline the preliminary speciication. In this case, language has the following ingredients: