# Interactive 3D Exploration of RDF Graphs through Semantic Planes
## 3 Use Cases
### Use Case #2: Exploring DBpedia
As stated at the beginning of this section, the WikiData query service is an example of the different ways of presenting the results of a SPARQL query (e.g., charts, tables, map, timeline, etc.). Another tool is RDF Gravity ([[http://semweb.salzburgresearch.at/apps/rdf-gravity/](http://semweb.salzburgresearch.at/apps/rdf-gravity/)]([http://semweb.salzburgresearch.at/apps/rdf-gravity/](http://semweb.salzburgresearch.at/apps/rdf-gravity/))). In a 2011 work, [PERSON] et al. ([[http://www.ebremer.com/nexus/2011-05-15](http://www.ebremer.com/nexus/2011-05-15)]([http://www.ebremer.com/nexus/2011-05-15](http://www.ebremer.com/nexus/2011-05-15))) investigated whether it would be possible to use semantics to enhance research collaborations within scientists sharing interests in their field. Their software, which the authors were unable to find and try, however, seems achievable with a wise use of Tarsier and might take advantage of the concept of semantic plane to get better visualization of the knowledge retrieved. LOD Live ([[http://en.lodlive.it/](http://en.lodlive.it/)]([http://en.lodlive.it/](http://en.lodlive.it/))) offers a service to browse RDF resources through the interaction with SPARQL endpoints (e.g., DBpedia). One can incrementally navigate the Linked Data starting from a selected resource. Around a resource, a set of symbols represents different kinds of relationship, such as direct relations, group of direct relations, inverse relations and group of inverse relations. A specific symbol is assigned to the owl:sameAs property (i.e., a very relevant aspect when dealing with heterogeneous data sources such as in the Linked Data domain). OWL visualization is also crucial with reference to ontology design. One of the most used tool in this sense is Protege ([[http://protege.stanford.edu/](http://protege.stanford.edu/)]([http://protege.stanford.edu/](http://protege.stanford.edu/))). The Protege ontology editor can be extended with plugins to visualize the ontology as a graph ([PERSON] et al., 2016; [PERSON] et al., 2016). This feature can be provided by plugins such as OntoGraf ([[http://protegewiki.stanford.edu/wiki/OWLviz](http://protegewiki.stanford.edu/wiki/OWLviz)]([http://protegewiki.stanford.edu/wiki/OWLviz](http://protegewiki.stanford.edu/wiki/OWLviz))) and Jambalaya ([[http://protegewiki.stanford.edu/wiki/Jambalaya](http://protegewiki.stanford.edu/wiki/Jambalaya)]([http://protegewiki.stanford.edu/wiki/Jambalaya](http://protegewiki.stanford.edu/wiki/Jambalaya))) (not supported by the last stable version of Protege). Ontograf allows to select a starting point in the ontology and then expand it to show subclass relations, instances, datatype and object properties. Different automated positioning methods are provided, but no repositioning and filtering mechanisms (e.g., based on SPARQL). OWLviz visualizes only classes and \"is-a\" relationships among them. Jambalaya (2016) is designed to show classes and instances, as well as relationships. Jambalaya also provides support for grouping nodes based on relationships (e.g., subclasses are represented as nested node of the superclass). [PERSON] and [PERSON] (2016) proposed a novel approach to the visualization of ontologies called cognitive frames. Through cognitive frames, the knowledge of a target concept related to the visualized fragment of ontology can be conveyed to the user. This approach is more focused on terminological data, rather than assertional data which are the main focus of our work. ## 6 Conclusions

This paper presents Tarsier, an interactive tool for the visualization of RDF knowledge bases with support for RDFS and OWL and its metaphore of Semantic planes that allows grouping all the RDF terms sharing common concepts. Semantic planes can be created, modified and split through a set of UI controls or through SPARQL 1.1 queries. The purpose of the presented tool is mainly to support: (1) students learning how to deal with Semantic Web data representation formats; and (2) software developers during the debugging of applications with RDF stores.