Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....of : are identified (explicit, strong and classical) and argues that, by its properties, explicit negation is preferable. By being a generalization of WFS for ELP which uses explicit negation, WFSX [PA92] appears as a natural candidate for the base semantics of our ELP PROLOPPE implementation. Alf93] make an extensive study on WFSX, and its relationship with several NMR formalisms. In [AP93b] WFSX is defined in terms of a logic of belief and provability , and compared with the works of [Che93, MT93, LS93] This open the way for contradiction removal (cf. below) and for generalizing WFSX to ....

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

....a methodology that uses a logic programming framework to model agents. Agent models are defined as logic programs extended with explicit negation and the semantics of the programs is given by the well founded semantics of logic programs with explicit negation (from Pereira et al. AP96; ADP95; Alf93 ] The well founded semantics has a complete and sound top down proof procedure with polynomial complexity and there is an implemented prototype ( DNP94 ] which allows us to obtain experimental results. In this paper we will show how some important behavior characteristics can be modeled by ....

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Faculdade de Ciencias e Tecnologia da Universidade Nova de Lisboa, 1993.

....choose a logic programming system that is able to associate more then one model to each program, the system for contradiction removal [14] 3. 1 Contradiction removal system The contradiction removal system is a triple hP; Rev; ICi, where: ffl P is a logic program extended with explicit negation [3, 1]. Definition 3.1 A program P extended with explicit negation is a set of rules: L 0 L 1 ; Lm ; not Lm 1 ; not L n with n m 0 and each L i is an objective literal, i.e. an atom A or its explicit negation :A; not is negation by failure. ffl Rev is a set of literals that can ....

....rule, i.e. not L is always true by CWA (closed world assumption) ffl IC is a set of integrity constraints Definition 3.3 A set of integrity constraints [14] is a set of rules: L 1 ; Lm ; not Lm 1 ; not L n with n m 0 and each L i is an objective literal, Definition 3. 4 [1] A program P is contradictory if and only the program does not have an Well Founded model for eXplicit negation, WFX. Definition 3.5 [14] hP; Rev; ICi is contradictory if and only if: ffl either P is contradictory, ffl or exists an integrity constraint in IC with the form: L 1 ; L n ....

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

....3. Let hM;Ri be a MNS, with R 6= fg; of a contradictory program P: Then R is a CRS of P: 4. Let P be a contradictory program with CRSs R 1 ; Rn : The sceptical revised program of P is P [ 8 : L not L j not L 2 [ 1in R i 9 = 11 The proof of correctness can be found in [2]. Thus in order to compute the minimal and sceptical submodels, one starts by computing all supports of : Although the definition of support requires one to know a priori the paraconsistent WFSX p ; an alternative definition exists such that this is not required. This definition is based on a ....

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993. 12 The implementation of such a preprocessor for the revision process above exists, and is available on request.

....It is argued there that explicit negation is preferable. The well founded semantics with explicit negation (WFSX) PA92] incorporates this prefered : negation, and also inherits the above mentioned desirable properties of WFS (e.g. cumulativity, relevance, bottom up fixpoint construction, cf. [Alf93]) However, as for the WFS of normal programs, the WFSX of extended programs too is by design overly careful in deciding about the falsity of some atoms, leaving them also undefined. Example 1 The extended program: win(X) move(X; Y ) not win(Y ) worthBetting(X) win(X) bet(X) ....

....to the WFSX of an extended program P: In section 4 we introduce tenability, define the O semantics for extended programs, and show that it accomplishes the goals we ve proposed. Finally we draw some comparisons with related work. Proofs of all theorems are omitted for brevity, and can be found in [Alf93]. 2 Preliminary definitions In this section we define the language of extended logic programs and briefly review the WFSX semantics [PA92] An extended program is a set of rules of the form: L 0 L 1 ; Lm ; not Lm 1 ; not Ln (0 m n) where each L i is an objective literal. ....

[Article contains additional citation context not shown here]

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

.... hand, for the class of theories resulting from some extended programs, the logic can be implemented using the top down procedures defined for WFSX[ADP94] Moreover, for this class, the logic enjoys the properties of cumulativity, rationality, relevance [Dix92] and others proven for WFSX in [Alf93]. In addition, the relationship also raises new issues in epistemic logics, and points towards their solution via the techniques in use in extended logic programming (cf. section 3) 2 Provability versus Knowledge Above we claimed logic EB is flexible and general. Next we express with it ....

.... program P by means of translation (4) augmented with the SW5 axioms for E : Then there is a one to one correspondence between expansions of T and the partial stable models of P of WFS with strong negation, as defined in [AP92] Comparisons between WFS with strong negation and WFSX, found in [AP92, Alf93], prove the former is less suitable for implementation (as it does not enjoy relevance [Dix92] is more credulous, and assigns semantics to less programs. Example 9 Program P : a a not b b not b translates into the theory: T = fE a; B Eb ) Ea; B Eb ) Ebg: Using logic K, there is one ....

Jos e J ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

....it is a better aproximation to answer sets than simply using WFS plus the renaming of : literals (cf. proposition 3.1) Thus, our top down method can be used as a sound one for answer sets, that provides less incompleteness than others. These and other properties of WFSX are detailed and proven in [6]. Since WFSX coincides with WFS on normal programs, our method is applicable to it and, for ground programs, compares favourably with previous approaches [2] To the best of our knowledge paper [62] is the only in the literature that addresses the topic of proof procedures for extended logic ....

....a distinctly different manner with respect to its original definition. This presentation is based on alternating fix points of Gelfond Lifschitz Gamma like operators [25, 27] The proof of equivalence between both definitions, as well as proofs of other results in this section, can be found in [6]. We begin by recalling the definition of Gamma: Definition 3.1 (The Gamma operator) Let P be an extended program, I an interpretation, and let P 0 (resp. I 0 ) be obtained from P (resp. I) by denoting every literal :A by a new atom, say : A. The GL transformation P 0 I 0 is the ....

[Article contains additional citation context not shown here]

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

....must be procedurally grounded on known facts. This requirement is conducive to a sceptical view of derived knowledge, which disallows jumping to conclusions when that is not called for. A formal analysis and clarification of the auto epistemic nature of extended logic programming can be found in [6, 5]. The widespread use of extended programs requires the definition of a correct top down querying mechanism, as for Prolog. One purpose of this paper is to present and exploit one such SLDNF like derivation procedure, SLX, for programs with explicit negation under well founded semantics (WFSX) ....

....operators, and the complexity for computing the stable models of a program is NP complete, even for DATALOG. in [2] Thus, our top down method can be used as a sound one for answer sets, that provides less incompleteness than others. These and other properties of WFSX are detailed and proven in [6]. Since WFSX coincides with WFS on normal programs, our method is applicable to it and, for ground programs, compares favourably with previous approaches [2] To the best of our knowledge paper [67] is the only in the literature that addresses the topic of proof procedures for extended logic ....

[Article contains additional citation context not shown here]

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

....nature readily allows pre processing into Prolog, showing promise as an efficient basis for further development. Since WFSX coincides with WFS on normal programs, our method is applicable to it and, for ground programs, compares favourably with previous approaches (cf. section 5) As proven in [1], WFSX is sound wrt to the answer sets semantics of [13] and it is a better aproximation to answer sets than simply using WFS plus the renaming of : literals (cf. example 2.2 where WFS plus the renaming of : literals yields fnot :b; not :cg and is properly included in WFSX) Thus, our ....

....then it must be assumed false by default. Here we present WFSX in a distinctly different manner with respect to its original definition, based on the application of the Gelfond Lifschitz 0 operator 2 and on a notion of semi normal programs. The equivalence between both definitions is proven in [1]. To impose the coherence requirement 3 we introduce: 1 This designation has been used in the literature instead of the more operational negation as failure (to prove) 2 For the definition of 0 see [13] 3 [1] shows the use of semi normal programs to impose coherence on partial stable ....

[Article contains additional citation context not shown here]

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

No context found.

Jos'e J'ulio Alferes. Semantics of Logic Programs with Explicit Negation. PhD thesis, Universidade Nova de Lisboa, October 1993.

Online articles have much greater impact   More about CiteSeer.IST   Add search form to your site   Submit documents   Feedback  

CiteSeer.IST - Copyright Penn State and NEC