We represent properties of actions in a logic programming language that uses both classical negation and negation as failure. The method is applicable to temporal projection problems with incomplete information, as well as to reasoning about the past. It is proved to be sound relative to a semantics of action based on states and transition functions. 1 Introduction This paper extends the work of Eshghi and Kowalski [6], Evans [7] and Apt and Bezem [1] on representing properties of actions in logic programming languages with negation as failure. Our goal is to overcome some of the limitations of the earlier work. The existing formalizations of action in logic programming are adequate for only the simplest kind of temporal reasoning---"temporal projection." In a temporal projection problem, we are given a description of the initial state of the world, and use properties of actions to determine what the world will look like after a series of actions is performed. Moreover, the existing ...

In this paper, we review recent work aimed at the application of declarative logic programming to knowledge representation in artificial intelligence. We consider exten- sions of the language of definite logic programs by classical (strong) negation, disjunc- tion, and some modal operators and show how each of the added features extends the representational power of the language.

The paper describes an extension of well-founded semantics for logic programs with two types of negation. In this extension information about preferences between rules can be expressed in the logical language and derived dynamically. This is achieved by using a reserved predicate symbol and a naming technique. Conflicts among rules are resolved whenever possible on the basis of derived preference information. The well-founded conclusions of prioritized logic programs can be computed in polynomial time. A legal reasoning example illustrates the usefulness of the approach. 1. Introduction: Why Dynamic Preferences are Needed Preferences among defaults play a crucial role in nonmonotonic reasoning. One source of preferences that has been studied intensively is specificity (Poole, 1985; Touretzky, 1986; Touretzky, Thomason, & Horty, 1991). In case of a conflict between defaults we tend to prefer the more specific one since this default provides more reliable information. E.g., if we know t...

this paper we show, however, that stationary expansions can be equivalently defined in terms of classical, 2-valued logic. As a byproduct, we obtain a simpler and more natural description of stationary expansions.

The realization of the Semantic Web vision, in which computational logic has a prominent role, has stimulated a lot of research on combining rules and ontologies, which are formulated in different formalisms, into a framework that is more useful for describing semantic content. In particular, combining logic programming with the Web Ontology Language (OWL), which is a standard based on description logics, emerged as an important issue for linking the Rules and Ontology Layers of the Semantic Web. Non-monotonic description logic programs (or dl-programs) were introduced for such a combination, in which a pair (L,P) of a description logic knowledge base L and a set of rules P with negation as failure is given a model-based semantics that generalizes the answer set semantics of logic programs. In this paper, we reconsider dl-programs and present a well-founded semantics for them as an analog for the other main semantics of logic programs. It generalizes the canonical definition of the well-founded semantics based on unfounded sets, and, as we show, lifts many of the well-known properties from ordinary logic programs to dl-programs. Among these properties: our semantics amounts to a partial model approximating the answer set semantics, which yields for positive and stratified dl-programs a total model coinciding with the answer set semantics; it has polynomial data complexity provided the access to the description logic

Recently the field of theory update has seen some improvement, in what concerns model updating, by allowing updates to be specified by so-called revision programs. The updating of theory models is governed by their update rules and also by inertia applied to those literals not directly affected by the update program. Though this is important, it remains necessary to tackle as well the updating of programs specifying theories. Some results have been obtained on the issue of updating a logic program which encodes a set of models, to obtain a new program whose models are the desired updates of the initial models. But here the program only plays the rôle of a means to encode the models. A logic program encodes much more than a set of models: it encodes knowledge in the form of the relationships between the elements of those models. In this paper we advocate that the principle of inertia is advantageously applied to the rules of the initial program rather than to the individual literals in...

Recently several authors have stressed and showed the importance of having a second kind of negation in logic programs for use in deductive databases, knowledge representation, and nonmonotonic reasoning [6, 7, 8, 9, 13, 14, 15, 24]. Different semantics for logic programs extended with :-negation (extended logic programs) have appeared [1, 4, 6, 9, 11, 12, 17, 19, 24] but, contrary to what happens with semantics for normal logic programs, there is no general comparison among them, specially in what concerns the use and meaning of the newly introduced :-negation. The goal of this paper is to contrast a variety of these semantics in what concerns their use and meaning of :-negation, and its relation to classical negation and to the default negation of normal programs, here denoted by not : To this purpose we define a parametrizeable schema to encompass and characterize a diversity of proposed semantics for extended logic programs, where the parameters are two: one the axioms AX: defin...

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Our purpose is to exhibit a modular systematic method of representing non-- monotonic reasoning problems with the Well Founded Semantics WFS of extended logic programs augmented with eXplicit negation (WFSX), augmented by its Contradiction Removal Semantics (CRSX) when needed. We apply this semantics, and its contradiction removal semantics counterpart, to represent non-monotonic reasoning problems. We show how to cast in the language of logic programs extended with explicit negation such forms of non-monotonic reasoning as defeasible reasoning, abductive reasoning and hypothetical reasoning and apply them to such different domains of knowledge representation as hierarchies and reasoning about actions. We then abstract a modular systematic method of representing non-monotonic problems in a logic programming semantics comprising two forms of negation avoiding some drawbacks of other proposals, with which we relate our work.

. Inspired by legal reasoning, this paper presents an argument-- based system for defeasible reasoning, with a logic--programming--like language, and based on Dung's argumentation--theoretic approach to the semantics of logic programming. The language of the system has both weak and explicit negation, and conflicts between arguments are decided with the help of priorities on the rules. These priorities are not fixed, but are themselves defeasibly derived as conclusions within the system. 1 Introduction This paper presents an argument--based system for defeasible reasoning, with a logic--programming--like language. Argument--based systems analyze defeasible reasoning in terms of the interactions between arguments for alternative conclusions. Defeasibility arises from the fact that arguments can be defeated by stronger counterarguments. Argumentation has proved to be a fruitful paradigm for formalising defeasible reasoning (cf. [13, 17, 18]). Not only does the notion of an argument natu...