Paraconsistent logics are examined as an approach to knowledge representation devoted to the formalization of reasoning in the presence of contradictions. the adequacy of paraconsistent logics in such a perspective is described both on a general level and on a more specific level: discussion involves representative examples as well as special features (in the form of logical principles) of some significant paraconsistent logics. There is also a comparison of the paraconsistent logics approach with two alternative approaches, namely belief revision and non-monotonic logics. © 1994 John Wiley & Sons, Inc.

Ordered logic programming is an extension of logic programming that includes, besides classical inference mechanisms, object-oriented abstractions and amenities for non- monotonic reasoning. Ordered logic programs are partially-ordered sets of ‘traditional’ logic programs where negation may also occur in the rule heads. The central issue of this paper is the definition of a new unifying semantics for ordered logic programs, called assumption-free semantics, capable of capturing different interesting semantics such as the well-founded and stable (partial model) semantics. It turns out that every ordered logic program possesses exactly one minimal assumption-free partial model which we call the well-founded partial model and one or more maximal assumption-free partial models called stable partial models. This stable model semantics can be viewed as taking the best of the previous approaches for ordered logic programs while keeping their (common) underlying intuition. We discuss the relationship between stable and well-founded partial models, the main result being that the intersection of all stable partial models is exactly the well-founded partial model in all cases but a special type of ordered logic programs.

An extension of logic programming, called “ordered logic programming”, which includes some abstractions of the object-oriented paradigm, is presented. An ordered program consists of a number of modules (objects), where each module is composed by a number of rules possibly with negated head predicates. A sort of “isa” hierarchy can be defined among the modules in order to allow for rule inheritance. Therefore, every module sees its own rules as local rules and the rules of the other modules to which it is connected by the “isa” hierarchy as global rules. In this way, as local rules may hide global rules, it is possible to deal with default properties and exceptions. This new approach represents a novel attempt to combine the logic paradigm with the object-oriented one in knowledge base systems. Moreover, this approach provides a new ground for explaining some recent proposals of semantics for classical logic programs with negation in the rule bodies and gives an interesting semantics to logic programs with negated rule heads.

We develop semantics for a logic, called ordered logic (OL), which models the most important aspects of object-oriented programming languages, such as object identity, multiple inheritance and defaults. The logic is based on a partially ordered structure of logical theories, which play the role of objects. OL is non-monotonic under the natural modeltheoretic semantics. A non-deterministic procedure is defined that has all models as fixpoints. It is shown that, for a well-behaved subclass of theories, this procedure can be used to generate exactly the set of ‘preferred’ models, where preference is based on the lack of ‘assumptions’. Classical logic programs with negation by failure are special cases of OL theories. From the above we can then derive a syntactic characterization of logic programs with stable models.

In this paper we present a user interface to the KIWI object oriented database system. The system combines ease of use with a powerful customisation facility which greatly simplifies the development of end-user applications. This is achieved by using the underlying object-oriented language (OOPS+) features such as inheritance to define a consistent and orthogonal set of graphical object classes that can be used to attach a tailor-made external representation of (a view on) objects and/or classes. In addition, using the same tools, it becomes a simple matter to define general purpose browsing and manipulation tools which otherwise would have to be developed separately.