Complexity and Expressiveness of ShEx for RDF

Slawomir Staworko (1) , Iovka Boneva (2, 1) , Jose Emilio Labra Gayo (3) , Samuel Hym (4) , Eric Gordon Prud'Hommeaux (5) , Harold Solbrig (6)

1 CRIStAL - Centre de Recherche en Informatique, Signal et Automatique de Lille - UMR 9189
2 LINKS - Linking Dynamic Data
3 Universidad de Oviedo [Oviedo]
4 2XS - Extra Small Extra Safe
5 CSAIL - Computer Science and Artificial Intelligence Laboratory [Cambridge]
6 Mayo Clinic [Scottsdale]

We study the expressiveness and complexity of Shape Expression Schema (ShEx), a novel schema formalism for RDF currently under development by W3C. 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.

Domaines: Base de données [cs.DB]; Web

Slawomir Staworko, Iovka Boneva, Jose Emilio Labra Gayo, Samuel Hym, Eric Gordon Prud'Hommeaux, et al.. Complexity and Expressiveness of ShEx for RDF. 18th International Conference on Database Theory (ICDT 2015), Mar 2015, Brussels, Belgium. ⟨10.4230/LIPIcs.ICDT.2015.195⟩. ⟨hal-01218552⟩