Updating logic programs

It is well known that rule-based knowledge bases are usually realized by logic programs. An update has to be performed to the current knowledge base if some new information occurs. In many applications associated with dynamic domains, however, such new information may occur not only as a set of simple facts but also a set of rules. In this paper, we view knowledge bases as extended logic programs [1] such that defeasible knowledge can be explicitly represented. We then consider the problem of how to update an extended logic program with another extended logic program while the former program represents the current knowledge base and the later one represents the new information that should be added to the current knowledge base. We show how the concept of priority associated with logic programs is employed to achieve our purpose. We also investigate semantical properties of logic program updates in detail.