Querying temporal and spatial constraint networks in PTIME

Koubarakis, M; Skiadopoulos, S

dc.contributor.author	Koubarakis, M	en
dc.contributor.author	Skiadopoulos, S	en
dc.date.accessioned	2014-03-01T01:15:51Z
dc.date.available	2014-03-01T01:15:51Z
dc.date.issued	2000	en
dc.identifier.issn	0004-3702	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/13764
dc.subject	constraint networks	en
dc.subject	constraint databases	en
dc.subject	temporal reasoning	en
dc.subject	spatial reasoning	en
dc.subject	tractable reasoning	en
dc.subject	computational complexity	en
dc.subject.classification	Computer Science, Artificial Intelligence	en
dc.subject.other	GLOBAL CONSISTENCY	en
dc.subject.other	INFORMATION	en
dc.subject.other	COMPLEXITY	en
dc.subject.other	KNOWLEDGE	en
dc.subject.other	REPRESENTATION	en
dc.subject.other	ALGORITHMS	en
dc.subject.other	DATABASES	en
dc.title	Querying temporal and spatial constraint networks in PTIME	en
heal.type	journalArticle	en
heal.identifier.primary	10.1016/S0004-3702(00)00055-2	en
heal.identifier.secondary	http://dx.doi.org/10.1016/S0004-3702(00)00055-2	en
heal.language	English	en
heal.publicationDate	2000	en
heal.abstract	We start with the assumption that temporal and spatial knowledge usually captured by constraint networks can be represented and queried more effectively by using the scheme of indefinite constraint databases. Because query evaluation in this scheme is in general a hard computational problem, we seek tractable instances of query evaluation. We assume that we have a class of constraints C with some reasonable computational and closure properties (the computational properties of interest are that the satisfiability problem and an appropriate version of the variable elimination problem for C should be solvable in PTIME). Under this assumption, we exhibit general classes of indefinite constraint databases and first-order modal queries for which query evaluation can be done with PTIME data complexity. We then search for tractable instances of C among the subclasses of Horn disjunctive linear constraints over the rationals. From previous research we know that the satisfiability problem for Horn disjunctive linear constraints is solvable in PTIME, but not the variable elimination problem. Thus we try to discover subclasses of Horn disjunctive linear constraints with tractable variable elimination problems. The class of UTVPInot equal constraints is the largest class that we show to have this property. Finally, we restate our general tractability results with C ranging over the newly discovered tractable classes. Interesting tractable query answering problems for indefinite temporal and spatial constraint databases are identified in this way. We close our complexity analysis by precisely outlining the frontier between tractable and possibly intractable query answering problems. (C) 2000 Elsevier Science B.V. All rights reserved.	en
heal.publisher	ELSEVIER SCIENCE BV	en
heal.journalName	ARTIFICIAL INTELLIGENCE	en
dc.identifier.doi	10.1016/S0004-3702(00)00055-2	en
dc.identifier.isi	ISI:000165320300007	en
dc.identifier.volume	123	en
dc.identifier.issue	1-2	en
dc.identifier.spage	223	en
dc.identifier.epage	263	en