Section: Research Program

Scalable and Expressive Techniques for the Semantic Web

The Semantic Web vision of a world-wide interconnected database of facts, describing resources by means of semantics, is coming within reach as the W3C's RDF (Resource Description Format) data model is gaining traction. The W3C Linking Open Data initiative has boosted the publication and interlinkage of a large number of datasets on the semantic web resulting to the Linked Open Data Cloud. These datasets of billions of RDF triples have been created and published online. Moreover, numerous datasets and vocabularies from different application domains are published nowadays as RDF graphs in order to facilitate community annotation and interlinkage of both scientific and scholarly data of interest. RDF storage, querying, and reasoning is now supported by a host of tools whose scalability and expressive power vary widely. Unsurprisingly, some of the most scalable tools draw upon the existing models and architecture for managing structured data. However, such tools often ignore the semantic aspects that make RDF interesting. For what concerns the semantics, a delicate balance must be found between expressive power and the efficiency of the resulting data management algorithms.

• The team works on identifying tractable dialects of RDF, amenable to highly efficient query answering algorithms, taking into account both data and semantics.

• Another line of research investigates the usage of RDF data and semantics to help structure, organize, and enrich structured documents from social media. Based on such a rich model, we devised novel query answering algorithms which attempt to explore efficiently the rich social dataset in order to return the most pertinent answers to the users, from a social, structured and semantic perspective. This research is related to the DigiCosme LabEx grant “Structured, Social and Semantic Search”.

• To help users get acquainted with large and complex RDF graphs, we have started to work on an approach for RDF graph summarization: a graph summary is a smaller RDF graph, often by several orders of magnitude, which preserves the core structural information of the original graph and thus allows to reason about several important graph property on a much more manageable structure.