Dynamic updates of non-monotonic knowledge bases

In this paper we investigate updates of knowledge bases represented by logi c programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in rule bodies but als o in their heads, We start by introducing the notion of an update P + U of one logic program P by another logic program U. Subsequently, we provide a precise semantic characterization of P + U, and study some basic properties of program updates, In particular, we show that our update programs genera lize the notion of interpretation update. We then extend this notion to com positional sequences of logic programs updates P-1 + P-2 + (. . .), definin g a dynamic program update, and thereby introducing the paradigm of dynamic logic programming. This paradigm significantly facilitates modularization of logic programming, and thus modularization of non-monotonic reasoning as a whole. Specifically, suppose that we are given a set of logic program mo dules, each describing a different state of our knowledge of the world. Dif ferent states may represent different time points or different sets of prio rities or perhaps even different viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to employ the mutual relationships ex isting between different modules to precisely determine, at any given modul e composition stage, the declarative as well as the procedural semantics of the combined program resulting from the modules. (C) 2000 Elsevier Science Inc. All rights reserved.