The concept of an agent has become important in both Artificial Intelligence (AI) and mainstream computer science. Our aim in this paper is to point the reader at what we perceive to be the most important theoretical and practical issues associated with the design and construction of intelligent agents. For convenience, we divide these issues into three areas (though as the reader will see, the divisions are at times somewhat arbitrary). Agent theory is concerned with the question of what an agent is, and the use of mathematical formalisms for representing and reasoning about the properties of agents. Agent architectures can be thought of as software engineering models of agents; researchers in this area are primarily concerned with the problem of designing software or hardware systems that will satisfy the prop-erties specified by agent theorists. Finally, agent languages are software systems for programming and experimenting with agents; these languages may embody principles proposed by theorists. The paper is not intended to serve as a tutorial introduction to all the issues mentioned; we hope instead simply to identify the most important issues, and point to work that elaborates on them. The article includes a short review of current and potential applications of agent technology.

The concept of an agent has recently become important in Artificial Intelligence (AI), and its relatively youthful subfield, Distributed AI (DAI). Our aim in this paper is to point the reader at what we perceive to be the most important theoretical and practical issues associated with the design and construction of intelligent agents. For convenience, we divide the area into three themes (though as the reader will see, these divisions are at times somewhat arbitrary). Agent theory is concerned with the question of what an agent is, and the use of mathematical formalisms for representing and reasoning about the properties of agents. Agent architectures can be thought of as software engineering models of agents; researchers in this area are primarily concerned with the problem of constructing software or hardware systems that will satisfy the properties specified by agent theorists. Finally, agent languages are software systems for programming and experimenting with agents; these languages typically embody principles proposed by theorists. The paper is not intended to serve as a tutorial introduction to all the issues mentioned; we hope instead simply to identify the key issues, and point to work that elaborates on them. The paper closes with a detailed bibliography, and some bibliographical remarks. 1

The needs of a real-time reasoner situated in an environment may make it appropriate to view error-correction and non-monotonicity as much the same thing. This has led us to formulate situated (or step) logic, an approach to reasoning in which the formalism has a kind of real-time self-reference that affects the course of deduction itself. Here we seek to motivate this as a useful vehicle for exploring certain issues in commonsensereasoning. In particular, a chief drawback of more traditional logics is avoided: from a contradiction we do not have all wffs swamping the (growing) conclusion set. Rather, we seek potentially inconsistent, but nevertheless useful, logics where the real-time self-referential feature allows a direct contradiction to be spotted and corrective action taken, as part of the same system of reasoning. Some specific inference mechanisms for real-time default reasoning are suggested, notably a form of introspection relevant to default reasoning. Special treatment of ...

THE aim of this thesis is to investigate logical formalisms for describing, reasoning about, specifying, and perhaps ultimately verifying the properties of systems composed of multiple intelligent computational agents. There are two obvious resources available for this task. The first is the (largely AI) tradition of reasoning about the intentional notions (belief, desire, etc.). The second is the (mainstream computer science) tradition of temporal logics for reasoning about reactive systems. Unfortunately, neither resource is ideally suited to the task: most intentional logics have little to say on the subject of agent architecture, and tend to assume that agents are perfect reasoners, whereas models of concurrent systems from mainstream computer science typically deal with the execution of individual program instructions. This thesis proposes a solution which draws upon both resources. It defines a model of agents and multi-agent systems, and then defines two execution models, which ...

We present a formalisation for the notion of viewpoint , a construct meant for expressing several varieties of relativised truth. The formalisation consists in a logic which extends first order predicate calculus through an axiomatization of provability and with the addition of proper reflection rules. The extension is not conservative, but consistency is granted. Viewpoints are defined as set of reified meta-level sentences. A proof theory for viewponts is developed which enables to carry out proofs of sentences involving several viewpoints. A semantic account of viewpoints is provided, dealing with issues of self referential theories and paradoxes, and exploiting the notion of contextual entailment . Notions such as beliefs, knowledge, truth and situations can be uniformly modeled as provability in specialised viewpoints, obtained by imposing suitable constraints on viewpoints.

Reflection is a wide-ranging concept that has been studied independently in many different areas of science in general, and computer science in particular. Even in the sub-area of programming languages, it has been applied to different paradigms, especially the logic, functional and objectoriented ones. Partly because of different past influences, but also because researchers in these communities scarcely talk to each others, concepts have evolved separately, sometimes to the point where it is hard for people in one community to recognize similarities in the work of others, not to speak about cross-fertilization among them. In this paper, we propose a synthesis covering mainly the application of computation reflection to programming languages. We compare the different approaches and try to identify similar concepts hidden behind different names or constructs. We also point out the different emphasis that has been given to different concepts in each of them. We do not claim neither comp...

It is common in the Knowledge Representation literature for a belief space to be considered to be a set of sentences. Some implications of this stance are examined, and an alternative view, that belief spaces are sets of propositions is developed, and found to be an improvement. This latter view requires that propositions be accepted as entities in the domain of discourse of languages of thought, which, it is argued, accords with commonsense usage. In exchange, the semantics of nested belief expressions is simplified, and certain problems caused by the sentential view are avoided. 1 Introduction What type of entity is the object of belief? Equivalently, if the "belief space" of a cognitive agent is the set of entities that the agent believes, what type of entities are the elements of that set? Two answers that have been suggested in the literature of Artificial Intelligence (AI) are sentences [Moore and Hendrix, 1982, Haas, 1986, Konolige, 1986, Genesereth and Nilsson, 1987, Perlis,...

In this review of metaprogramming in logic we pay equal attention to theoretical and practical issues: the contents range from mathematical and logical preliminaries to implementation and applications in, e.g., software engineering and knowledge representation. The area is one in rapid development but we have emphasized such issues that are likely to be important for future metaprogramming languages and methodologies. 1 Introduction The term `metaprogramming' relates to `programming' as `metalanguage' relates to `language' and `metalogic' to `logic': programming where the data represent programs. It should be no surprise that metaprogramming with logic programming languages takes advantage of many results from metalogic. In the most general interpretation we would say that `metaprogramming ' refers to any kind of computer programming where the input or output represents programs. We will refer to a program of this kind as a metaprogram and to its data as object programs. Analogousl...

The kind of resource limitation that is most evident in commonsense reasoners is the passage of time while the reasoner reasons. There is not necessarily any fixed and final set of consequences with which such a reasoning agent ends up. In formalizing commonsense reasoners, then, one must be able to take into account that time is passing as the reasoner is reasoning. The reasoner can then make use of such information in subsequent deductions. Step-logic is such a formalism. It was developed in [Elgot-Drapkin, 1988] to model the ongoing process of deduction. Conclusions are drawn step-by-step. There is no "final" state of reasoning; the emphasis is on intermediate conclusions. In this paper we use step-logic to model the Three-wise-men Problem. Although others have formalized this problem, they have ignored the time aspect that is inherent in the problem: a correct assessment of the situation is made by recognizing that the reasoning process takes time and determining that the other wis...

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