User-Centered Incremental Data Exploration and Visualization

In this paper we present Paged Graph Visualization (PGV), a new user-centered, semi-autonomous visualization tool for RDF data exploration, validation and examination. PGV consists of two main components: the PGV visualizer, which is the front-end of PGV, and the BRAHMS data-store, which is our high performance main-memory RDF storage system. Unlike the existing graph visualization techniques which attempt to display the entire graph, PGV has been designed for the incremental, semantics-driven exploration of very large RDF ontologies. A novel, Ferris-Wheel-like visualization technique is used to explore the so called hot spots in the graph, i.e. nodes with large numbers (hundreds) of immediate neighbors. In response to the user-controlled, semantics-driven direction of the exploration, the PGV visualizer obtains the necessary sub-graphs from BRAHMS and enables their incremental visualization without having to rearrange the previously laid out subgraphs. PGV and BRAHMS communicate via the HTTP protocol and to provide the necessary on-line response times, BRAHMS is connected to the Web server via the Fast-CGI interface which eliminates the need of restarting the BRAHMS process at every request. Additionally, PGV has been enhanced with a speech recognizer and a speech synthesizer.