Casual reasoning in planning1

Reasoning about actions necessarily involves tracking the truth of assertions about the world over time. The SIPE planning system retains the efficiency of the STRIPS assumption for this while enhancing expressive power by allowing the specification of a causl theory. Separation of knowledge about causality from knowledge about actions relieves operators of much of their representational burden and allows them to be applicable in a wide range of contexts. The implementation of causal theories is described, together with examples and evaluations of the system's expressive power and efficiency.     

Considerations on default logic: an alternative approach1

In the following paper we analyze Reiter's default logic and suggest modifying the notion of an extension for default theories. This modification leads to two important properties which are not guaranteed in Reiter's formalism: the existence of extensions and semimonotonicity.     

Expressiveness and tractability in knowledge representation and reasoning1

A fundamental computational limit on automated reasoning and its effect on knowledge representation is examined. Basically, the problem is that it can be more difficult to reason correctly with one representational language than with another and, moreover, that this difficulty increases dramatically as the expressive power of the language increases. This leads to a tradeoff between the expressiveness of a representational language and its computational tractability. Here we show that this tradeoff can be seen to underlie the differences among a number of existing representational formalisms, in addition to motivating many of the current research issues in knowledge representation.     

Modeling the user's conceptual knowledge in BGP-MS,a user modeling shell system1

The paper describes the modeling of a user's conceptual knowledge in the general user modeling shell system BGP-MS. On the one hand, BGP-MS is a workbench for the develment of a user model in a particular application domain. It supports the definition of the architecture of the individual user model, and of the architecture and the contents of user stereotypes. A rich representation language for conceptual knowledge, a partition mechanism, and flexible graphics-based interfaces are at the disposal of the user model developer. On the other hand, BGP-MS is a runtime user modeling tool aimed at fulfilling central tasks of a user modeling component in an application system. In this mode, the system offers a functional interface for accessing and updating the model of the current user, as well as basic domain-independent inference mechanisms, support for inferences defined by the developer, and a customizable stereotype management utility. The usefulness of BGP-MS will be demonstrated by illustrating how it can support the user modeling of various recently developed application systems.