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Computationally tractable planning problems reported in the literature so far have almost exclusively been deened by syntactical restrictions. To better exploit the inherent structure in problems, it is probably necessary to study also structural restrictions on the underlying state-transition graph. The exponential size of this graph, though, makes such(More)
We present a class of planning instances such that the plan existence problem is tractable while plan generation is prov-ably intractable for instances of this class. The class is deened by simple structural restrictions, all of them testable in polynomial-time. Furthermore, we show that plan generation can be carried out in solution-polynomial time, that(More)
We i n vestigate the computational properties of the spatial algebra RCC-5 which is a restricted version of the RCC framework for spatial reasoning. The satissability problem for RCC-5 is known to be NP-complete but not much i s k n o wn about its approximately four billion subclasses. We provide a complete classiication of satissability for all these(More)
Allen's interval algebra is one of the best established formalisms for temporal reasoning. This article provides the final step in the classification of complexity for satisfiability problems over constraints expressed in this algebra. When the constraints are chosen from the full Allen's algebra, this form of satisfiability problem is known to be(More)
There has been a tremendous advance in domain-independent planning over the past decades, and planners have become increasingly efficient at finding plans. However, this has not been paired by any corresponding improvement in detecting unsolvable instances. Such instances are obviously important but largely neglected in planning. In other areas, such as(More)
Planning with incomplete information may mean a numberof diierent thingss that certain facts of the initial state are not known, that operators can have random or nondeterministic eeects, or that the plans created contain sensing operations and are branching. Study of the complexity of incomplete information planning has so far been concentrated on(More)
Many combinatorial search problems can be expressed as 'constraint satisfaction problems'. This class of problems is known to be NP-hard in general, but a number of restricted constraint classes have been identified which ensure tractability. This paper presents the first general results on combining tractable constraint classes to obtain larger, more(More)
This paper combines two important directions of research in temporal reson-ing: that of nding maximal tractable subclasses of Allen's interval algebra, and that of reasoning with metric temporal information. Eight new maximal tractable subclasses of Allen's interval algebra are presented, some of them subsuming previously reported tractable algebras. The(More)