Bernhard Nebel

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We describe and evaluate the algorithmic techniques that are used in the FF planning system Like the HSP system FF relies on forward state space search using a heuristic that estimates goal distances by ignoring delete lists Unlike HSP s heuristic our method does not assume facts to be independent We introduce a novel search strategy that combines hill(More)
We have previously reported a number of tractable planning problems de ned in the SAS formalism. This article complements these results by providing a completemap over the complexity of SAS planning under all combinations of the previously considered restrictions. We analyze the complexity both of nding a minimal plan and of nding any plan. In contrast to(More)
Computational tractability has been a major concern in the area of termi-nological knowledge representation and reasoning. However, all analyses of the computational complexity of terminological reasoning are based on the hidden assumption that subsumption in terminologies reduces to subsumption of concept descriptions without a signiicant increase in(More)
We introduce a new subclass of Allen's interval algebra we call “ORD-Horn subclass,” which is a strict superset of the “pointisable subclass.” We prove that reasoning in the ORD-Horn subclass is a polynomial-time problem and show that the path-consistency method is sufficient for deciding satisfiability. Further, using an extensive(More)
The computational properties of qualitative spatial reasoning have been investigated to some degree. However, the question for the boundary between polynomial and NP-hard reasoning problems has not been addressed yet. In this paper we explore this boundary in the \Region Connection Calculus" RCC-8. We extend Bennett's encoding of RCC-8 in modal logic. Based(More)
1. Introduction Qualitative reasoning is an approach for dealing with commonsense knowledge without using numerical computation. Instead, one tries to represent knowledge using a limited vocabulary such as qualitative relationships between entities or qualitative categories of numerical values, for instance, using {+, −, 0} for representing real values. An(More)
We consider diierent methods of optimizing the classiication process of terminological representation systems, and evaluate their eeect on three diierent types of test data. Though these techniques can probably be found in many existing systems, until now there has been no coherent description of these techniques and their impact on the performance of a(More)
Terminological knowledge representation formalisms are intended to capture the analytic relationships between terms of a vocabulary intended to describe a domain. A term whose deenition refers, either directly or indirectly, to the term itself presents a problem for most terminological representation systems because it is obvious neither whether such a term(More)