Querying Distributed RDF Data Sources with SPARQL

Querying Distributed RDF Data Sources with SPARQL
Querying Distributed RDF Data Sources with SPARQL
Bibliographical Metadata
Subject:	Querying Distributed RDF Data Sources
Year:	2008
Authors:	Bastian Quilitz, Ulf Leser
Venue	ESWC
Content Metadata
Problem:	SPARQL Query Federation
Approach:	decompose a query into sub-queries, each of which can be answered by an individual service.
Implementation:	DARQ
Evaluation:	Evaluate the performance of the DARQ query engine.

Abstract

DARQ provides transparent query access to multiple SPARQL services, i.e., it gives the user the impression to query one single RDF graph despite the real data being distributed on the web. A service description language enables the query engine to decompose a query into sub-queries, each of which can be answered by an individual service. DARQ also uses query rewriting and cost-based query optimization to speed-up query execution.

Conclusion

DARQ offers a single interface for querying multiple, distributed SPARQL end-points and makes query federation transparent to the client. One key feature of DARQ is that it solely relies on the SPARQL standard and therefore is compatible to any SPARQL endpoint implementing this standard. Using service descriptions provides a powerful way to dynamically add and remove endpoints to the query engine in a manner that is completely transparent to the user. To reduce execution costs we introduced basic query optimization for SPARQL queries. Our experiments show that the optimization algorithm can drastically improve query performance and allow distributed answering of SPARQL queries over distributed sources in reasonable time. Because the algorithm only relies on a very small amount of statistical information we expect that further improvements are possible using techniques. An important issue when dealing with data from multiple data sources are differences in the used vocabularies and the representation of information. In further work, we plan to work on mapping and translation rules between the vocabularies used by different SPARQL endpoints. Also, we will investigate generalizing the query patterns that can be handled and blank nodes and identity relationships across graphs.

Future work

In further work, we plan to work on mapping and translation rules between the vocabularies used by different SPARQL endpoints. Also, we will investigate generalizing the query patterns that can be handled and blank nodes and identity relationships across graphs.

Approach

Positive Aspects: Query rewriting and cost-based query optimization to speed-up query execution.

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Implementations

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GUI: No

Research Problem

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RelatedProblem: transparent query federation

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Evaluation

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