Semantic Navigation on the Web of Data

The increasing availability of structured data on the Web stimulated a renewed interest in its graph nature. Applications like the Google Knowledge Graph (KG) [227] and the Facebook Graph (FG) [192] build large graphs of entities (e.g., people, places) and their semantic relations (e.g., born in, located in). The KG, by matching keywords in a search request against entities in the graph, enhances Google’s results with structured data in the same spirit of Wikipedia info boxes. The FG by looking at semantic relations between Facebook entities enables searching within this huge social graph. However, both approaches adopt proprietary architectures with idiosyncratic data models and limited support in terms of APIs to access their data and querying capabilities. A precursor of these applications is the Linked Open Data project [275] (see Section 1.6 in Chapter 1). The openness of data and the ground on Web technologies are among the driving forces of Linked Open Data. There is an active community of developers that build applications and APIs both to convert and consume linked data in the Resource Description Framework (RDF) standard data format. These initiatives, which maintain structured information at each node in the Web graph and semantic links between nodes, are making the Web evolve toward a Web of Data (WoD). Fig. 11.1 provides a pictorial representation of the traditional Web and the WoD by looking at the latter from the Linked Open Data perspective. Although sharing a graph-like nature, there are some