Modeling Complex Domains of Actions and Change

This paper studies the problem of modeling complex domains of actions and change within high-level action description languages. We investigate two main issues of concern: (a) can we represent complex domains that capture together different problems such as ramifications, non-determinism and concurrency of actions, at a high-level, close to the given natural ontology of the problem domain and (b) what features of such a representation can affect, and how, its computational behaviour. The paper describes the main problems faced in this representation task and presents the results of an empirical study, carried out through a series of controlled experiments, to analyze the computational performance of reasoning in these representations. The experiments compare different representations obtained, for example, by changing the basic ontology of the domain or by varying the degree of use of indirect effect laws through domain constraints. This study has helped to expose the main sources of computational difficulty in the reasoning and suggest some methodological guidelines for representing complex domains. Although our work has been carried out within one particular high-level description language, we believe that the results, especially those that relate to the problems of representation, are independent of the specific modeling language.