Datalog programs and their persistency numbers

Afrati, F; Cosmadakis, S; Foustoucos, E

dc.contributor.author	Afrati, F	en
dc.contributor.author	Cosmadakis, S	en
dc.contributor.author	Foustoucos, E	en
dc.date.accessioned	2014-03-01T01:22:02Z
dc.date.available	2014-03-01T01:22:02Z
dc.date.issued	2005	en
dc.identifier.issn	15293785	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/16459
dc.subject	Bounded-tree width hypergraphs	en
dc.subject	Boundedness	en
dc.subject	Datalog	en
dc.subject	Finite automata	en
dc.subject	Persistency numbers	en
dc.subject	Persistent variables	en
dc.subject	Program transformations	en
dc.subject.other	Bounded-tree width hypergraphs	en
dc.subject.other	Boundedness	en
dc.subject.other	Datalog	en
dc.subject.other	Decision problems	en
dc.subject.other	Languages	en
dc.subject.other	Models of computation	en
dc.subject.other	Persistency numbers	en
dc.subject.other	Persistent variables	en
dc.subject.other	Program transformations	en
dc.subject.other	Resource-bounded	en
dc.subject.other	Algorithms	en
dc.subject.other	Computational methods	en
dc.subject.other	Database systems	en
dc.subject.other	Finite automata	en
dc.subject.other	Formal languages	en
dc.subject.other	Graph theory	en
dc.subject.other	Logic programming	en
dc.subject.other	Query languages	en
dc.subject.other	Computer programming	en
dc.title	Datalog programs and their persistency numbers	en
heal.type	journalArticle	en
heal.identifier.primary	10.1145/1071596.1071597	en
heal.identifier.secondary	http://dx.doi.org/10.1145/1071596.1071597	en
heal.publicationDate	2005	en
heal.abstract	The relation between Datalog programs and homomorphism problems and between Datalog programs and bounded treewidth structures has been recognized for some time and given much attention recently. Additionally, the essential role of persistent variables (of program expansions) in solving several relevant problems has also started to be observed. It turns out that to understand the contribution of these persistent variables to the difficulty of some expressibility problems, we need to understand the interrelationship among different notions of persistency numbers, some of which we introduce and/or formalize in the present work. This article is a first foundational study of the various persistency numbers and their interrelationships. To prove the relations among these persistency numbers, we had to develop some nontrivial technical tools that promise to help in proving other interesting results too. More precisely, we define the adorned dependency graph of a program, a useful tool for visualizing sets of persistent variables, and we define automata that recognize persistent sets in expansions. We start by elaborating on finer definitions of expansions and queries, which capture aspects of homomorphism problems on bounded treewidth structures. The main results of this article are (a) a program transformation technique, based on automata-theoretic tools, which manipulates persistent variables (leading, in certain cases, to programs of fewer persistent variables); (b) a categorization of the different roles of persistent variables; this is done by defining four notions of persistency numbers which capture the propagation of persistent variables from a syntactical level to a semantical one; (c) decidability results concerning the syntactical notions of persistency numbers that we have defined; and (d) the exhibition of new classes of programs for which boundedness is undecidable. © 2005 ACM.	en
heal.journalName	ACM Transactions on Computational Logic	en
dc.identifier.doi	10.1145/1071596.1071597	en
dc.identifier.volume	6	en
dc.identifier.issue	3	en
dc.identifier.spage	481	en
dc.identifier.epage	518	en