ExpLOD: Exploring Interlinking and RDF Usage in the Linked Open Data Cloud

The Linking Open Data community project is promoting the creation of interlinked RDF datasets with links between data items identified using dereferenceable URIs. This promising direction for publishing data on the web brings forward a number of issues. A key challenge is to understand the data, the schema, and the interlinks that are actually used both within and across linked datasets. Understanding actual RDF usage is critical in the increasingly common situations where terms from many different vocabularies are mixed (potentially with no consistent RDFS or OWL schema). In this paper we propose a novel mechanism to describe RDF usage by combining neighborhood defining queries with bisimilar contractions to produce bisimulation contractions of neighbourhoods (or BCNs). We present algorithms for computing BCNs and describe a tool, ExpLOD, that supports constructing and visualizing BCNs. ExpLOD can also generate SPARQL queries based on the BCNs. We use ExpLOD to describe RDF usage within several of the collections from the Linked Open Data cloud.