摘要:

“Simpson's paradox,” first described nearly a century ago, is an anomaly that sometimes arises from pooling data. Dramatic instances of the paradox have occurred in real life in the domains of epidemiology and admissions policies. Many writers have recently described hypothetical examples of the paradox arising in other areas of life and it seems possible that the paradox may occur frequently in mundane domains but with less serious implications. Thus, it is not surprising that the paradox should arise in commonsense reasoning, that subarea of artificial intelligence that seeks to axiomatize reasoning in such mundane domains. It arises as the problem “approximate proof by cases” and the question of whether to accept it may well depend on whether we wish to construct performance or competence models of reasoning. This article gives a brief history of the paradox and discusses its occurrence in our own discipline. It argues that if the paradox occurs frequently but undramatically in real life, every uncertain reasoning system will have to deal with the problem in s

ISSN:0824-7935    

DOI:10.1111/j.1467-8640.1995.tb00021.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

In this paper we present various logical characterizations of justification‐based (nonmonotonic) truth maintenance systems (JTMS). These characterizations, which are proved to be equivalent, aim at describing dependency‐directed backtracking (DDB) (i.e., the process of resolving conflicts which can arise when nogoods are allowed in the set of justifications), mainly relying on the intuitive idea that a contrapositrve use of justifications is needed to resolve inconsistencies. The idea is first formalized by means of the notion of three‐valued labeling and then through a transformation which explicitly adds all contrapositives of the justifications. An abductive characterization of the JTMS is provided through a further transformation which converts a set of nonmonotonic justifications to a corresponding abduction framework. This approach provides a unifying framework, based on the notion of abduction, for describing both JTMSs and assumption‐based TMSs

ISSN:0824-7935    

DOI:10.1111/j.1467-8640.1995.tb00022.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The epistemic notions of knowledge and belief have most commonly been modeled by means of possible worlds semantics. In such approaches an agent knows (or believes) all logical consequences of its beliefs. Consequently, several approaches have been proposed to model systems ofexplicit belief,more suited to modeling finite agents or computers. In this paper a general framework is developed for the specification of logics of explicit belief. A generalization of possible worlds, called situations, is adopted. However the notion of an accessibility relation is not employed; instead a sentence is believed if theexplicit propositionexpressed by the sentence appears among a set of propositions associated with an agent at a situation. Since explicit propositions may be taken as corresponding to “belief contexts” or “frames of mind,” the framework also provides a setting for investigating such approaches to belief. The approach provides a uniform and flexible basis from which various issues of explicit belief may be addressed and from which systems may be contrasted and compared. A family of logics is developed using this framework, which extends previous approaches and addresses issues raised by these earlier approaches. The more interesting of these logics are tractable, in that determining if a belief follows from a set of beliefs, given certain assumptions, can be accomplished in polynomi

ISSN:0824-7935    

DOI:10.1111/j.1467-8640.1995.tb00023.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Ordered model trees were introduced as a normal form for disjunctive deductive databases. They were also used to facilitate the computation of minimal models for disjunctive theories by exploiting the order imposed on the Herbrand base of the theory. In this work we show how the order on the Herbrand base can be used to compute perfect models of a disjunctive stratified finite theory. We are able to compute the stable models of a general finite theory by combining the order on the elements of the Herbrand base with previous results that had shown that the stable models of a theoryTcan be computed as the perfect models of a corresponding disjunctive theory ɛTresulting from applying the so called evidential transformation toT.While other methods consider many models that are rejected at the end, the use of atom ordering allows us to guarantee that every model generated belongs to the class of models being computed. As for negation‐free databases, the ordered tree serves as the canonical representation of the databa

ISSN:0824-7935    

DOI:10.1111/j.1467-8640.1995.tb00024.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

We present the syntax and proof theory of a logic of argumentation, LA. We also outline the development of a category theoretic semantics for LA. LA is the core of a proof theoretic model for reasoning under uncertainty. In this logic, propositions are labeled with a representation of the arguments which support their validity. Arguments may then be aggregated to collect more information about the potential validity of the propositions of interest. We make the notion of aggregation primitive to the logic, and then define strength mappings from sets of arguments to one of a number of possible dictionaries. This provides a uniform framework which incorporates a number of numerical and symbolic techniques for assigning subjective confidences to propositions on the basis of their supporting arguments. These aggregation techniques are also described with examples.

ISSN:0824-7935    

DOI:10.1111/j.1467-8640.1995.tb00025.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Negotiations are very important in a multiagenl environment, particularly, in an environment where there are conflicts between the agents, and cooperation would be beneficial. We have developed a general structure for aNegotiating Automated Agentthat consists of five modules: a Prime Minister, a Ministry of Defense, a Foreign Office, a Headquarters and Intelligence. These modules are implemented using a dynamic set of local agents belonging to the different modules. We used this structure to develop a Diplomacy player.Diplomat.Playing Diplomacy involves a certain amount of technical skills as in other board games, but the capacity to negotiate, explain, convince, promise, keep promises or break them, is an essential ingredient in good play.Diplomatwas evaluated and consistently played better than human players.

ISSN:0824-7935    

DOI:10.1111/j.1467-8640.1995.tb00026.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

In this paper, we present VSTA, our Prolog‐based verifier, for formal specification and verification of systolic architectures. VSTA allows users to design systolic array architectures in the STA specification language (STA was developed earlier by Ling for formal description and reasoning of systolic designs) and semi‐automatically verifies these designs The implementation of VSTA is based on a standard Prolog system. Its interface uses Motif system calls based on the X11 and UNIX environments. VSTA provides facilities to assist the user in the design of systolic array specifications. The system allows a formal proof to be derived interactively with suggestions from the user. The proof techniques used are mathematical induction and rewriting. The induction technique is adopted to exploit the regularity and locality nature of systolic array architectures. A number of verification tactics are developed and their operational rules are used in the verifier. Using the powerful symbolic computation ability of Prolog, particularly pattern matching, automatic backtracking, and depth‐first searching, the verifier performs efficiently in the construction of proofs. We also describe the strategies we used in proving a matrix multiplication systolic array and an LU decomposition systolic

ISSN:0824-7935    

DOI:10.1111/j.1467-8640.1995.tb00027.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY