A universal fixpoint semantics for ordered logic

Ordered logic is the theoretical foundation of the LOCO programing language [9] which combines the declarative elegance and power of logic programming with asvantages of object-oriented systems. Ordered logic is based on a partially ordered structure of logical theories or objects. Objects are entities that may contain positive as well as negative information represented by rules. The partial order allows for the definition of a preference structure on these objects and consequently also on the information they contain.  The result is a simple yet powerful logic that models classical as well as non-monotonic inference mechanisms. The central issue of this paper is the definition of a universal fixpoint semantics for ordered logic programs which constitutes an important extension and generalization of the fixpoint semantics prresented in [11, in the sense that it computes all partial models (well-founded and stable partial models included) instead of only ´total´ models (a possibly empty subset of the stable partial models), thus overcoming the limitations of the previous approach

Applying AI techniques for patent information retrieval

This report presents an overview of recent developments in software technology, especially information retrieval and expert systems. Particular consideration is given to the possible applications in the area of user-friendly access to patent information systems. A proposal for an expert system, that could act as a knowledgeable intermediary between the end user with no information retrieval experience and the various host systems, is described.

Preferred Answer Sets for Ordered Logic Programs

We extend answer set semantics to deal with inconsistent programs (containing classical negation), by finding a "best" answer set. Within the context of inconsistent programs, it is natural to have a partial order on rules, representing a preference for satisfying certain rules, possibly at the cost of violating less important ones. We show that such a rule order induces a natural order on extended answer sets, the minimal elements of which we call preferred answer sets. We characterize the expressiveness of the resulting semantics and show that it can simulate negation as failure as well as disjunction. We illustrate an application of the approach by considering database repairs, where minimal repairs are shown to correspond to preferred answer sets