Mapping the central LOD ontologies to PROTON upper-level ontology

Linking Open Data (LOD) facilitates the emergence of a web of linked data by publishing and interlinking open data on the web in RDF. One can explore linked data across servers by following the links in the graph. The LOD cloud has 203 datasets and more than 14 billion RDF triples (http://lod-cloud.net). This paper describes an approach to access these data by means of a single ontology, matched to the schemata describing several of the most common LOD datasets. They are presented in a reason-able view - FactForge (http://factforge.net) - the biggest and most heterogeneous body of factual knowledge on which inference is performed. Techniques of (a) making matching rules with "ontology expressions", (b) adding new instances with inference rules, and (c) extending the upper level ontology with classes and properties are employed. They succeed to align ontologies designed according to different principles and displaying conceptual and structural mismatches.