Abstract

The paper discusses some properties of system descriptions in action language – a recent extension of action language by defined fluents. We give a sufficient condition guaranteeing that states of an system description are fully determined by statics and inertial fluents. In system descriptions satisfying this condition, defined fluents simply facilitate the description of dynamic domains; they are not essential and can be eliminated. We use our sufficient condition to identify a common core of action languages and. This is an expansion of the work of, who identified a common core of languages and. The results presented in this paper are based on the close relationship between action languages and the theory of logic programs under the answer set semantics.