TIME-DEPENDENT CONCEPTS - REPRESENTATION AND REASONING USING TEMPORALDESCRIPTION LOGICS

A time-dependent concept is a conceptual entity that is defined in ter ms of temporal relationships with other entities. For example, the con cept of an action is defined in terms of a set of temporal relationshi ps among states of a system. The concept of ''widow'', in natural lang uage, is defined in terms of events that have occurred in the past. Ti me-dependent concepts appear in several application areas, from natura l language to diagnosis, from planning to data mining. An interesting issue in knowledge representation is how to formally represent and rea son with these concepts. In this paper, we represent a family of forma l representation languages obtained as an interval-based temporal exte nsion of description logics. We illustrate the expressiveness of these formalisms in representing time-dependent concepts with respect to st andard description logics and other extensions. We give some complexit y results for reasoning problems and we propose approximate algorithms to compute subsumption among time-dependent concepts.