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The Challenge of Optional Matching in SPARQL

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Foundations of Information and Knowledge Systems (FoIKS 2016)

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Abstract

Conjunctive queries are arguably the most widely used querying mechanism in practice and the most intensively studied one in database theory. Answering a conjunctive query (CQ) comes down to matching all atoms of the CQ simultaneously into the database. As a consequence, a CQ fails to provide any answer if the pattern described by the query does not exactly match the data. CQs might thus be too restrictive as a querying mechanism for data on the web, which is considered as inherently incomplete. The semantic web query language SPARQL therefore contains the OPTIONAL operator as a crucial feature. It allows the user to formulate queries which try to match parts of the query over the data if available, but do not destroy answers of the remaining query otherwise. In this article, we have a closer look at this optional matching feature of SPARQL. More specifically, we will survey several results which have recently been obtained for an interesting fragment of SPARQL – the so-called well-designed SPARQL graph patterns.

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Notes

  1. 1.

    We use here the algebraic-style notation from [29] rather than the official SPARQL syntax of [33]. In particular, we explicitly use an AND operator (rather than comma-separated lists) to denote conjunctions.

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Acknowledgments

This work was supported by the Vienna Science and Technology Fund (WWTF), project ICT12-15 and by the Austrian Science Fund (FWF): P25207-N23 and W1255-N23.

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Correspondence to Reinhard Pichler .

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Ahmetaj, S., Fischl, W., Kröll, M., Pichler, R., Šimkus, M., Skritek, S. (2016). The Challenge of Optional Matching in SPARQL. In: Gyssens, M., Simari, G. (eds) Foundations of Information and Knowledge Systems. FoIKS 2016. Lecture Notes in Computer Science(), vol 9616. Springer, Cham. https://doi.org/10.1007/978-3-319-30024-5_10

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  • DOI: https://doi.org/10.1007/978-3-319-30024-5_10

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