Star-like auto-configurable layouts of variable radius for visualizing and exploring RDF/S ontologies

The visualization of ontologies is a challenging task especially if they are large. In this paper we propose a visualization approach which is based on star-like graphs of variable radius which enables users to gradually explore and navigate through the entire ontology without overloading them. The star-like graphs are visualized using a Force Directed Placement algorithm (FDP) specially suited for RDF schemas whose configuration parameters can be adjusted interactively by the end-user via an intuitive on-screen tool bar. In addition, and since each star-like graph exhibits different graph features, we propose a novel automatic configuration method for the FDP algorithm parameters that is based on a number of quality metrics (area density and verticality of subclass hierarchies) and corresponding corrective actions. The experimental evaluation showed the quality of the yielded layout is significantly improved and the proposed approach is acceptably fast for real-time exploration. The user study showed that users prefer these views and perform various very common tasks faster.

► We propose star-like graphs of variable radius for gradually exploring large ontologies.
► The layout is computed by a Force Directed Placement algorithm appropriate for RDFS.
► We propose a novel method for the automatic configuration of the layout algorithm.
► We report various experimental results including the results of a user study.