Time-dependent concepts: Representation and reasoning using temporal description logics

A time-dependent concept is a conceptual entity that is defined in terms of temporal relationships with other entities. For example, the concept of an action is defined in terms of a set of temporal relationships among states of a system. The concept of ''widow'', in natural language, is defined in terms of events that have occurred in the past. Time-dependent concepts appear in several application areas, from natural language to diagnosis, from planning to data mining. An interesting issue in knowledge representation is how to formally represent and reason with these concepts. In this paper, we represent a family of formal representation languages obtained as an interval-based temporal extension of description logics. We illustrate the expressiveness of these formalisms in representing time-dependent concepts with respect to standard description logics and other extensions. We give some complexity results for reasoning problems and we propose approximate algorithms to compute subsumption among time-dependent concepts.