The Space-Efficient Core of Vadalog

Gerald Berger, Georg Gottlob, Andreas Pieris, Emanuel Sallinger

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract / Description of output

Vadalog is a system for performing complex reasoning tasks such as those required in advanced knowledge graphs. The logical core of the underlying Vadalog language is the warded fragment of tuple-generating dependencies (TGDs). This formalism ensures tractable reasoning in data complexity, while a recent analysis focusing on a practical implementation led to the reasoning algorithm around which the Vadalog system is built. A fundamental question that has emerged in the context of Vadalog is the following: can we limit the recursion allowed by wardedness in order to obtain a formalism that provides a convenient syntax for expressing useful recursive statements, and at the same time achieves space-efficiency? After analyzing several real-life examples of warded sets of TGDs provided by our industrial partners, as well as recent benchmarks, we observed that recursion is often used in a restricted way: the body of a TGD contains at most one atom whose predicate is mutually recursive with a predicate in the head. We show that this type of recursion, known as piecewise linear in the Datalog literature, is the answer to our main question. We further show that piece-wise linear recursion alone, without the wardedness condition, is not enough as it leads to the undecidability of reasoning. We finally study the relative expressiveness of the query languages based on (piece-wise linear) warded sets of TGDs.
Original languageEnglish
Title of host publicationPODS '19 Proceedings of the 38th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems
Place of PublicationNew York
Number of pages15
ISBN (Print)978-1-4503-6227-6
Publication statusE-pub ahead of print - 25 Jun 2019
EventACM SIGMOD/PODS International Conference on Management of Data (SIGMOD 2019) - Amsterdam, Netherlands
Duration: 30 Jun 20195 Jul 2019


ConferenceACM SIGMOD/PODS International Conference on Management of Data (SIGMOD 2019)
Abbreviated titleSIGMOD 2019
Internet address

Keywords / Materials (for Non-textual outputs)

  • reasoning
  • query answering
  • Datalog
  • tuple-generating dependencies
  • complexity
  • expressive power


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