Thesis (M. Phil.)--University of Hong Kong, 1992.

Cognitive Science attempts to study entities which in some sense possess beliefs, intentions, desires etc. The preferred term in this thesis for such entities is agents. An attempt at a scientific analysis of agents however throws up a number of questions. What are the right concepts to describe agents? What kinds of formal notations permit perspicuous reasoning about agents? What can be said about the architecture and construction of agents? The introductory section of this thesis discusses these questions in some detail, using Dennett's ideas about intentional systems [Den87] as a point of departure. I then examine a number of studies from Artificial Intelligence, Logic, Natural Language semantics and Philosophy which give shape to the current state of the art in agent theory. This leads to the development of a mathematical model of multi-object/agent interaction, which I call the SRS-model (SRS - Synchronous Reactive Systems). I demonstrate the adequacy of the model by using it to formalise learning and games scenarios. Next, various logics are introduced which capture input-output and then belief-desire level descriptions of agents. These logics are given an SRS-model semantics, and adequacy is shown by modelling a psychological experiment (an agent in a Skinner Box). It is shown how the example can be formally analysed in terms of mechanisms and architecture at the SRS-level (including a computer simulation); at the level of behaviourism (using a temporal logic - APTL); and at an intentional level (using an epistemic-conative temporal logic ECTL). Some remarks are made about extending the analysis to multi-agent situations involving co-operation, competition and dialogue. Finally, a detailed survey is made of the main mathematical and logical resources available to the style of formal cognitive science advocated in this thesis. I include modal logic, including its epistemic and doxastic variants; the extension of modal logic to dynamic logic; and the various approaches recently developed in the logic of time.

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Kowalski's connection graph method provides a representation for logic programs which allows for the incorporation of better procedural control techniques than standard logic programming languages. A proposed search strategy for visual recognition which combines top-down and bottom-up techniques has been incorporated in a connection graph implementation. The connection graph representation also allows for the natural incorporation of constraint satisfaction techniques in logic programming. Kowalski's approach to incorporating constraint satisfaction techniques in connection graphs is examined in detail. It is shown that his approach is not efficient enough to be used as a general preprocessing algorithm but that a modified version may be of use. Increased control of search and the incorporation of consistency techniques increase the procedural adequacy of logic programs for representing knowledge without compromising the descriptive capacity of the form. / Science, Faculty of / Computer Science, Department of / Graduate

A new declarative language is presented which captures the expressibility of both logic programming languages and functional languages. This is achieved by conditional graph rewriting, with full unification as the parameter passing mechanism. The syntax and semantics are described both formally and informally, and examples are offered to support the expressibility claim made above. The language design is of further interest due to its uniformity and the inclusion of a novel mechanism for type inference in the presence of derived type hierarchies

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