Logic-based representation and reasoning for user modeling shell systems

Core services of user modeling shell systems :include the provision of repr esentations for user model contents and for other relevant knowledge, and o f reasoning mechanisms. These representation and reasoning facilities shoul d be powerful and flexible, in order to satisfy both complex and specialize d needs that developers of user modeling; systems may have. This article fi rst identifies these needs through a comprehensive overview of logic-based representation and reasoning in user modeling system. Then, the AsTRa (Assu mption Type Representation) framework for logic-based user model representa tion and reasoning is presented. This framework obtains its power and flexi bility through an integration of the two main scientific approaches that we re pursued to date, namely the partition approach and the modal logic appro ach. The central notion of the framework is the 'assumption type', a partit ion-like partial knowledge base for storing all assumptions about the user that are of the same type. Within assumption types, logic-based representat ion formalisms can be employed. The semantics of assumption types and conte nt formalisms can be characterized in terms of modal logic, so that an exte nsion to full modal logic is possible. Moreover, special mechanisms for han dling so-called 'negative assumptions' are developed, which are also firmly grounded in modal logic semantics. The paper concludes with a description of the user modeling shell BGP-MS as a prototypical implementation of AsTRa , and a discussion of the approach in the light of other user modeling shel ls.