Detecting Unsatisfiable Pattern Queries under Shape Expression Schema

Shiori Matsuoka, Nobutaka Suzuki

Abstract

Among queries for RDF/graph data, pattern query is the most popular and important one. A pattern query that returns empty answer for every valid graph is clearly useless, and such a query is called unsatisfiable. Formally, we say that a pattern query q is unsatisfiable under a schema S if there is no valid graph g of S such that the result of q over g is nonempty. It is desirable that unsatisfiable pattern queries can be detected efficiently before being executed since unsatisfiable query may require much execution time but always reports empty answer. In this paper, we focus on Shape Expression (ShEx) as schema, and we propose an algorithm for detecting unsatisfiable pattern queries under a given ShEx schema. Experimental results suggest that our algorithm can determine the satisfiability of pattern query efficiently.

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