Action Languages - a Tool for Modeling Dynamic Systems

In this talk I give a short introduction into theory and applications of action languages - simple logical formalisms for modeling dynamic system. A theory (action description) of an action language defines a transition diagram containing all possible trajectories of the system. Due to the size of the diagram, the problem of finding its concise specification is not trivial and has been a subject of research for a comparatively long time. Its solution requires the good understanding of the nature of causal effects of actions in the presence of complex interrelations between fluents (propositions whose truth value may depend on the state of the system). An additional level of complexity is added by the need to specify what is not changed by actions. The latter, known as the frame problem, is often reduced to the problem of finding a concise and accurate representation of the inertia axiom, a default which says that things normally stay as they are. The search for such a presentation substantially influenced AI research during the last twenty years. In this talk, I present the syntax and semantics of an action language, called AL, give the relationship between AL and the language of logic programs under the answer set/stable model semantics, and explain how this relationship can be used for building intelligent agents capable of planning, diagnostics, and other interesting types of reasoning.