Complexity and Expressiveness of ShEx for RDF

Authors Slawek Staworko, Iovka Boneva, Jose E. Labra Gayo, Samuel Hym, Eric G. Prud'hommeaux, Harold Solbrig

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Slawek Staworko
Iovka Boneva
Jose E. Labra Gayo
Samuel Hym
Eric G. Prud'hommeaux
Harold Solbrig

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Slawek Staworko, Iovka Boneva, Jose E. Labra Gayo, Samuel Hym, Eric G. Prud'hommeaux, and Harold Solbrig. Complexity and Expressiveness of ShEx for RDF. In 18th International Conference on Database Theory (ICDT 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 31, pp. 195-211, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)


We study the expressiveness and complexity of Shape Expression Schema (ShEx), a novel schema formalism for RDF currently under development by W3C. A ShEx assigns types to the nodes of an RDF graph and allows to constrain the admissible neighborhoods of nodes of a given type with regular bag expressions (RBEs). We formalize and investigate two alternative semantics, multi- and single-type, depending on whether or not a node may have more than one type. We study the expressive power of ShEx and study the complexity of the validation problem. We show that the single-type semantics is strictly more expressive than the multi-type semantics, single-type validation is generally intractable and multi-type validation is feasible for a small (yet practical) subclass of RBEs. To curb the high computational complexity of validation, we propose a natural notion of determinism and show that multi-type validation for the class of deterministic schemas using single-occurrence regular bag expressions (SORBEs) is tractable.
  • RDF
  • Schema
  • Graph topology
  • Validation
  • Complexity
  • Expressiveness


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