4,030 research outputs found
A Complete Classification of Tractability in RCC-5
We investigate the computational properties of the spatial algebra RCC-5
which is a restricted version of the RCC framework for spatial reasoning. The
satisfiability problem for RCC-5 is known to be NP-complete but not much is
known about its approximately four billion subclasses. We provide a complete
classification of satisfiability for all these subclasses into polynomial and
NP-complete respectively. In the process, we identify all maximal tractable
subalgebras which are four in total.Comment: See http://www.jair.org/ for an online appendix and other files
accompanying this articl
Reachability in Cooperating Systems with Architectural Constraints is PSPACE-Complete
The reachability problem in cooperating systems is known to be
PSPACE-complete. We show here that this problem remains PSPACE-complete when we
restrict the communication structure between the subsystems in various ways.
For this purpose we introduce two basic and incomparable subclasses of
cooperating systems that occur often in practice and provide respective
reductions. The subclasses we consider consist of cooperating systems the
communication structure of which forms a line respectively a star.Comment: In Proceedings GRAPHITE 2013, arXiv:1312.706
On tractability and congruence distributivity
Constraint languages that arise from finite algebras have recently been the
object of study, especially in connection with the Dichotomy Conjecture of
Feder and Vardi. An important class of algebras are those that generate
congruence distributive varieties and included among this class are lattices,
and more generally, those algebras that have near-unanimity term operations. An
algebra will generate a congruence distributive variety if and only if it has a
sequence of ternary term operations, called Jonsson terms, that satisfy certain
equations.
We prove that constraint languages consisting of relations that are invariant
under a short sequence of Jonsson terms are tractable by showing that such
languages have bounded relational width
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