Agent theories and architectures.

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