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Semantic acyclicity on graph databases

Published:22 June 2013Publication History

ABSTRACT

It is known that unions of acyclic conjunctive queries (CQs) can be evaluated in linear time, as opposed to arbitrary CQs, for which the evaluation problem is NP-complete. It follows from techniques in the area of constraint-satisfaction problems that "semantically acyclic" unions of CQs -- i.e., unions of CQs that are equivalent to a union of acyclic ones -- can be evaluated in polynomial time, though testing membership in the class of semantically acyclic CQs is NP-complete.

We study here the fundamental notion of semantic acyclicity in the context of graph databases and unions of conjunctive regular path queries with inverse (UC2RPQs). It is known that unions of acyclic C2RPQs can be evaluated efficiently, but it is by no means obvious whether the same holds for the class of UC2RPQs that are semantically acyclic. We prove that checking whether a UC2RPQ is semantically acyclic is decidable in 2EXPSPACE, and that it is EXPSPACE-hard even in the absence of inverses. Furthermore, we show that evaluation of semantically acyclic UC2RPQs is fixed-parameter tractable. In addition, our tools yield a strong theory of approximations for UC2RPQs when no equivalent acyclic UC2RPQ exists.

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    • Published in

      cover image ACM Conferences
      PODS '13: Proceedings of the 32nd ACM SIGMOD-SIGACT-SIGAI symposium on Principles of database systems
      June 2013
      334 pages
      ISBN:9781450320665
      DOI:10.1145/2463664
      • General Chair:
      • Richard Hull,
      • Program Chair:
      • Wenfei Fan

      Copyright © 2013 ACM

      Publisher

      Association for Computing Machinery

      New York, NY, United States

      Publication History

      • Published: 22 June 2013

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      PODS '13 Paper Acceptance Rate24of97submissions,25%Overall Acceptance Rate476of1,835submissions,26%

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