Browsing by Subject "Logic programming languages"

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Automated reasoning about actions
(2005) Lee, Joohyung; Lifschitz, Vladimir
The study of reasoning about a tions is an important subarea of the theory of ommonsense reasoning. It is on erned with developing appropriate systems of logi for des ribing a tions and their e e ts on the world. In spite of the fa t that this reasoning is based on ommon sense and does not involve any spe ialized knowledge, attempts to formalize it using lassi al logi en ountered serious diÆ ulties, whi h have led to the emergen e of a new eld, nonmonotoni logi s. In parti ular, M Cain and Turner introdu ed the ausal logi in whi h the notions of \being aused" and \being true" are distinguished. Based on their logi , Giun higlia and Lifs hitz proposed a high level a tion language C, whi h is a formal model of parts of natural language that are used for des ribing properties of a tions. The ausal logi and C, along with the on ept of satis ability planning, provided us with a widely appli able and eÆ ient method of automated reasoning about a tions, whi h led to the reation of the Causal Cal ulator (CCal ). vii In this dissertation, we have identi ed several essential limitations of the M Cain{Turner ausal logi and a tion language C. To over ome these limitations, we de ned an extension of the ausal logi to multi-valued formulas and a new a tion language C+. Language C+ an represent non-propositional uents, de ned uents, additive uents, rigid onstants, and defeasible ausal laws. Se ond, we have redesigned and reimplemented CCal to a ount for these extensions, and tested the new CCal and the underlying theory by applying them to several new, more diÆ ult examples of ommonsense reasoning. The input language of the new CCal is more elaboration tolerant than the old version. Last, we have shown how to turn ausal logi into propositional logi based on the idea of \loop formulas" that originated from logi programming under the answer set semanti s.
Expressiveness of answer set languages
(2007) Ferraris, Paolo, 1972-; Lifschitz, Vladimir
Answer set programming (ASP) is a form of declarative programming oriented towards difficult combinatorial search problems. It has been applied, for instance, to plan generation and product configuration problems in artificial intelligence and to graph-theoretic problems arising in VLSI design and in historical linguistics. Syntactically, ASP programs look like Prolog programs, but the computational mechanisms used in ASP are different: they are based on the ideas that have led to the development of fast satisfiability solvers for propositional logic. ASP is based on the answer set/stable model semantics for logic problems, originally intended as a specification for query answering in Prolog. From the original definition of 1988, the semantics was independently extended by different research groups to more expressive kinds of programs, with syntax and semantics that are incompatible with each other. In this thesis we study how the various extensions are related to each other. In order to do that, we propose another definition of an answer set. This definition has three main characteristics: (i) it is very simple, (ii) its syntax is more general than the usual concept of a logic program, and (iii) strong theoretical tools can be used to reason on it. About (ii), we show that our syntax allows constructs defined in many other extensions of the answer sets semantics. This fact, together with (iii), allows us to study the expressiveness of those constructs. We also compare the answer set semantics with another important formalism developed by Norm McCain and Hudson Turner, called logic.