SMJoin: A multi-way join operator for SPARQL queries

Mikhail Galkin, Kemele M. Endris, Maribel Acosta, Diego Collarana, Maria Esther Vidal, Sören Auer

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

6 Scopus citations


Join operators are particularly important in SPARQL query engines that collect RDF data using Web access interfaces. State-of-The-Art SPARQL query engines rely on binary join operators tailored for merging results from SPARQL queries over Web access interfaces. However, in queries with a large number of triple patterns, binary joins constitute a significant burden on the query performance. Multi-way joins that handle more than two inputs are able to reduce the complexity of pre-processing stages and reduce the execution time. Whereas in the relational databases -eld multi-way joins have already received some attention, the applicability of multiway joins in SPARQL query processing remains unexplored. We devise SMJoin, a multi-way non-blocking join operator tailored for independently merging results from more than two RDF data sources. SMJoin implements intra-operator adaptivity, i.e., it is able to adjust join execution schedulers to the conditions of Web access interfaces; thus, query answers are produced as soon as they are computed and can be continuously generated even if one of the sources becomes blocked. We empirically study the behavior of SMJoin in two benchmarks with queries of di-erent selectivity; state-of-The-Art SPARQL query engines are included in the study. Experimental results suggest that SMJoin outperforms existing approaches in very selective queries, and produces first answers as fast as compared adaptive query engines in non-selective queries.

Original languageEnglish
Title of host publicationProceedings of the 13th International Conference on Semantic Systems, SEMANTiCS 2017
EditorsRinke Hoekstra, Victor de Boer, Tassilo Pellegrini, Rinke Hoekstra, Catherine Faron-Zucker
PublisherAssociation for Computing Machinery
Number of pages8
ISBN (Electronic)9781450352963
StatePublished - 11 Sep 2017
Externally publishedYes
Event13th International Conference on Semantic Systems, SEMANTiCS 2017 - Amsterdam, Netherlands
Duration: 12 Sep 201713 Sep 2017

Publication series

NameACM International Conference Proceeding Series


Conference13th International Conference on Semantic Systems, SEMANTiCS 2017


  • Join algorithms
  • Multi-way Join Operators


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