Monadic Datalog Containment
نویسندگان
چکیده
We reconsider the problem of containment of monadic datalog (MDL) queries in unions of conjunctive queries (UCQs). Prior work has dealt with special cases, but has left the precise complexity characterization open. We begin by establishing a 2EXPTIME lower bound on the MDL/UCQ containment problem, resolving an open problem from the early 90’s. We then present a general approach for getting tighter bounds on the complexity, based on analysis of the number of mappings of queries into tree-like instances. We use the machinery to present an important case of the MDL/UCQ containment problem that is in co-NEXPTIME, and a case that is in EXPTIME. We then show that the technique can be used to get a new tight upper bound for containment of tree automata in UCQs. We show that the new MDL/UCQ upper bounds are tight.
منابع مشابه
Containment of Monadic Datalog Programs via Bounded Clique-Width
Containment of monadic datalog programs over data trees (labelled trees with an equivalence relation) is undecidable. Recently, decidability was shown for two incomparable fragments: downward programs, which never move up from visited tree nodes, and linear childonly programs, which have at most one intensional predicate per rule and do not use descendant relation. As di erent as the fragments ...
متن کاملContainment in Monadic Disjunctive Datalog, MMSNP, and Expressive Description Logics
We study query containment in three closely related formalisms: monadic disjunctive Datalog (MDDLog), MMSNP (a logical generalization of constraint satisfaction problems), and ontology-mediated queries (OMQs) based on expressive description logics and unions of conjunctive queries. Containment in MMSNP was known to be decidable due to a result by Feder and Vardi, but its exact complexity has re...
متن کاملMonadic Datalog Containment on Trees
We show that the query containment problem for monadic datalog on finite unranked labeled trees can be solved in 2-fold exponential time when (a) considering unordered trees using the axes child and descendant, and when (b) considering ordered trees using the axes firstchild, nextsibling, child, and descendant. When omitting the descendant-axis, we obtain that in both cases the problem is Expti...
متن کاملA note on monadic datalog on unranked trees
In the article Recursive queries on trees and data trees (ICDT’13), Abiteboul et al. asked whether the containment problem for monadic datalog over unordered unranked labeled trees using the child relation and the descendant relation is decidable. This note gives a positive answer to this question, as well as an overview of the relative expressive power of monadic datalog on various representat...
متن کاملMonadic Datalog Containment on Trees Using the Descendant-Axis
In their AMW’14-paper, Frochaux, Grohe, and Schweikardt showed that the query containment problem for monadic datalog on finite unranked labeled trees is Exptime-complete when (a) considering unordered trees using the child-axis, and when (b) considering ordered trees using the axes firstchild, nextsibling, and child. Furthermore, when allowing to use also the descendant-axis, the query contain...
متن کاملTesting Query Containment in the Presence of Binding Restrictions
In information-integration systems, sources have diverse and limited query capabilities. In a recent paper [LC00], we showed that sources not mentioned in a query can contribute to the query result by providing useful bindings. We studied connection queries, where each connection query is a natural join of distinct source views with the necessary selection and projection. Some optimization prob...
متن کامل