SemQA: SPARQL with idempotent disjunction

E. Patrick Shironoshita, Yves R. Jean-Mary, Ray M. Bradley, Mansur R. Kabuka

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


The SPARQL LeftJoin abstract operator is not distributive over Union; this limits the algebraic manipulation of graph patterns, which in turn restricts the ability to create query plans for distributed processing or query optimization. In this paper, we present semQA, an algebraic extension for the SPARQL query language for RDF, which overcomes this issue by transforming graph patterns through the use of an idempotent disjunction operator Or as a substitute for Union. This permits the application of a set of equivalences that transform a query into distinct forms. We further present an algorithm to derive the solution set of the original query from the solution set of a query where Union has been substituted by Or. We also analyze the combined complexity of SPARQL, proving it to be NP-complete. It is also shown that the SPARQL query language is not, in the general case, fixed-parameter tractable. Experimental results are presented to validate the query evaluation methodology presented in this paper against the SPARQL standard to corroborate the complexity analysis and to illustrate the gains in processing cost reduction that can be obtained through the application of semQA.

Original languageEnglish (US)
Pages (from-to)401-414
Number of pages14
JournalIEEE Transactions on Knowledge and Data Engineering
Issue number3
StatePublished - Mar 2009


  • Ontology languages
  • Query languages
  • Query processing

ASJC Scopus subject areas

  • Computational Theory and Mathematics
  • Information Systems
  • Computer Science Applications


Dive into the research topics of 'SemQA: SPARQL with idempotent disjunction'. Together they form a unique fingerprint.

Cite this