Julien Leblay

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We consider the setting of a Semantic Web database, containing both explicit data encoded in RDF triples, and implicit data, implied by the RDF semantics. Based on a query workload, we address the problem of selecting a set of views to be materialized in the database, minimizing a combination of query processing, view storage, and view maintenance costs.(More)
The increasing interest in the RDF data model has turned the efficient processing of queries over RDF datasets to a challenging and crucial task. Indeed, the triple format of the RDF data model, along with the lack of structure that characterizes it, raise new challenges in data management both in terms of performance and scalability. In this paper, we(More)
In recent years, the significant growth of RDF data used in numerous applications has made its efficient and scalable manipulation an important issue. In this paper, we present RDFViewS, a system capable of choosing the most suitable views to materialize, in order to minimize the query response time for a specific SPARQL query workload, while taking into(More)
Since the beginning of the Semantic Web initiative, significant efforts have been invested in finding efficient ways to publish, store, and query metadata on the Web. RDF and SPARQL have become the standard data model and query language, respectively, to describe resources on the Web. Large amounts of RDF data are now available either as stand-alone(More)
Traditional query processing involves a search for plans formed by applying algebraic operators on top of primitives representing access to relations in the input query. But many querying scenarios involve two interacting issues that complicate the search. On the one hand, the search space may be limited by access restrictions associated with the interfaces(More)
Fact checking and data journalism are currently strong trends. The sheer amount of data at hand makes it difficult even for trained professionals to spot biased, outdated or simply incorrect information. We propose to demonstrate FactMinder, a fact checking and analysis assistance application. SIGMOD attendees will be able to analyze documents using(More)
The data needed to answer queries is often available through Webbased APIs. Indeed, for a given query there may be many Webbased sources which can be used to answer it, with the sources overlapping in their vocabularies, and differing in their access restrictions (required arguments) and cost. We introduce PDQ (ProofDriven Query Answering), a system for(More)
When querying RDF data, one may use reasoning to reach intensional data, i.e., data defined by sets of rules. This is usually achieved through forward chaining, with space and maintenance overheads, or backward chaining, with high query evaluation and optimization costs. Recent approaches rely on pre-computing the <i>terminological closure</i> of the data(More)