Executing SPARQL Queries over the Web of Linked Data

Abstract

Abstract. The Web of Linked Data forms a single, globally distributed dataspace. Due to the openness of this dataspace, it is not possible to know in advance all data sources that might be relevant for query answering. This openness poses a new challenge that is not addressed by traditional research on federated query processing. In this paper we present an approach to execute SPARQL queries over the Web of Linked Data. The main idea of our approach is to discover data that might be relevant for answering a query during the query execution itself. This discovery is driven by following RDF links between data sources based on URIs in the query and in partial results. The URIs are resolved over the HTTP protocol into RDF data which is continuously added to the queried dataset. This paper describes concepts and algorithms to implement our approach using an iterator-based pipeline. We introduce a formalization of the pipelining approach and show that classical iterators may cause blocking due to the latency of HTTP requests. To avoid blocking, we propose an extension of the iterator paradigm. The evaluation of our approach shows its strengths as well as the still existing challenges.

Top-k Linked Data Query Processing

“…In previous work [10,11], push-based execution using symmetric hash join operators was shown to have better performance than pullbased implementations (such as [6]). In a push-based model, operators push their results to subsequent operators instead of pulling from input operators, i.e., the execution is driven by the incoming data.…”

“…Previous work on Linked Data query processing focused on processing basic graph patterns (BGP), which is a core feature of SPARQL. [6,5] can be performed at runtime. The link traversal strategy assumes that Q contains at least one URI d as "entry point" to G. Starting from triples in T d , G is then searched for results by following links from d to other sources.…”

“…To obtain the dataset, we executed all queries directly over the Web of Linked Data using a link-traversal approach [6] and recorded all Linked Data sources that were retrieved during execution. In total, we downloaded 681,408 Linked Data sources, comprising a total of 1,867,485 triples.…”

“…In this context, researchers have studied the problem of Linked Data query processing [3,5,6,10,11,16]. Processing structured queries over Linked Data can be seen as a special case of federated query processing.…”

Publishing and Consuming Provenance Metadata on the Web of Linked Data

“…it includes links to voiD descriptions etc.) then provenance can be queried using the link traversal based query execution paradigm [8] as implemented in SQUIN 6 . This query approach evaluates SPARQL queries as in Example 2 over a dataset that is continuously augmented with Linked Data objects from the Web.…”