A Visual Aide for Understanding Endpoint Data

In order to pose queries on SPARQL endpoints, users need to understand the underlying structure of the data that is stored. Unfortunately, and despite the importance of endpoints in the Semantic Web infrastructure, in most (if not all) publicly available endpoints the only way of understanding this structure is by performing a considerable number of probe queries, perhaps inspired in a few examples that are also made available. This paper looks into the problem of providing additional information for SPARQL-fluent users that need to query a RDF dataset they are not familiar with. We set up to understand what is the essential information that a user needs to query a SPARQL dataset, and then propose a visualisation that can effectively help users learn this information. This visualisation consists of a labelled graph whose nodes are the different types of entities in the RDF dataset, and where two types are related if entities of these types appear related in the RDF dataset. We illustrate our visualisation using the Linked Movie Database dataset.