# Interactive 3D Exploration of RDF Graphs through Semantic Planes
## 3 Use Cases
### Use Case #2: Exploring DBpedia
We were not able to load the datasets we would like to test but only the ones conforming with the BioPAX format ([[http://www.biopax.org/](http://www.biopax.org/)]([http://www.biopax.org/](http://www.biopax.org/))). Moving to the research works more related to ontologies and Linked Data visualization, among all the papers we have been able to go through, citedSayers2004 first attempted to visualize and interact with an RDF graph using a web browser: the aim was to visualize only a portion of interest through a research over literals. An incremental graph navigation method is presented by [PERSON] and [PERSON] (2007) that proposed what they call \"node merging\" as a way to include into a vertex, not only its label, but also a list of incoming and outgoing edges. In addition, [PERSON] et al. (2010) proposed a tool implementing an incremental algorithm to layout the explored sub-graphs. Focusing on not ontology-expert users, [PERSON] et al. (2011) presented a visual language based on a set of graphical primitives and a color scheme (VOWL 2). Instances are not considered in this tool, although their number can be shown for the selected class. An example of a tool implementing VOWL 2 is provided by WebOWL ([[http://vowl.visualdataweb.org/webvowl.html](http://vowl.visualdataweb.org/webvowl.html)]([http://vowl.visualdataweb.org/webvowl.html](http://vowl.visualdataweb.org/webvowl.html))). Another tool in this context is tFacet ([[http://www.visualdataweb.org/tfacet.php](http://www.visualdataweb.org/tfacet.php)]([http://www.visualdataweb.org/tfacet.php](http://www.visualdataweb.org/tfacet.php))) that has been presented by [PERSON] and [PERSON] (2016) and is based on the concept of faceted exploration ([PERSON], 2016). Facets can be extracted through SPARQL queries to SPARQL endpoints and, also in this case the exploration starts with the limitation of the initial search space to avoid displaying very large amount of data. Focusing on relationships discovery between two or more nodes, [PERSON] et al. (2016) presented RelFinder ([[http://www.visualdataweb.org/relfinder.php](http://www.visualdataweb.org/relfinder.php)]([http://www.visualdataweb.org/relfinder.php](http://www.visualdataweb.org/relfinder.php))), a tool that implements a process consisting in four steps: object mapping, relationship search, visualization, and interactive exploration. A last example of a tool designed for not expert users is presented by [PERSON] and [PERSON] (2016). This tool aims at combining scatter plots (i.e., to support the visual identification of linear correlations, clusters, patterns, and extreme values) with the interaction metaphor of magic lenses ([PERSON], 2016). For a general discussion on a model designed to describe and thus better understand the human-computer interaction in the Semantic Web, we invite the reader to refer to the paper by [PERSON] et al. (2016). To the best of our knowledge, [PERSON] and [PERSON] (2016) and [PERSON] et al. (2016) published two of the most recent papers on semantic data visualization. In the former, the authors investigated on different approaches for exploratory discovery and analysis of Linked Data provided by a set of tools, while the latter authors focused on presenting a tool based on a novel approach to Linked Data exploration named Encyclopedic Knowledge Patterns (EKPs). We conclude this section by presenting a set of tools that we think can be representative of the ones specifically designed for ontology and Linked Data visualization. The first is the query service offered by WikiData ([[https://query.wikidata.org/](https://query.wikidata.org/)]([https://query.wikidata.org/](https://query.wikidata.org/))): the user can formulate a SPARQL query and the results are shown in many different ways, including a graph. Using the graph representation, the user can navigate the graph by clicking on each node. Every click opens the direct relationships with other nodes (i.e., first by presenting the number of resources).