# Interactive 3D Exploration of RDF Graphs through Semantic Planes
In this article, we propose Tarsier: an interactive and ontology agnostic tool for the 3D visualization of RDF graphs. Tarsier implements all the above-mentioned features and it allows partitioning the KB into semantic planes. A semantic plane can be defined as a set of RDF terms sharing a common meaning and it can be created directly or indirectly through standard SPARQL 1.1 queries. We argue that this approach would help to understand or extract the structure of represented data by following a common mental approach: splitting the KB among planes, each of them related to a specific concept. The user can incrementally build a view by adding and/or removing information according to its actual needs and splitting the information among planes. Relationships among resources in different planes are in such a way emphasized. Furthermore, the user may still maintain a view on the rest of the knowledge base, if needed. To the best of the authors' knowledge, none of the existing tools provides a similar feature and we argue that many application domains may benefit of a multiplanar visualization. Eventually, Tarsier is also suitable to view reified knowledge bases [8], since it allows the distinction among the raw triples, the statements reifying them and the information about the statements (i.e., meta information). Very poor support to reification is currently provided by the existing tools. The idea of Tarsier is grounded on the authors' experience in teaching Semantic Web technologies in the \"Interoperability of Embedded Systems\" course held at the School of Engineering and Architecture of the University of Bologna. The course is focused on the application of Semantic Web data representation means to context-aware IoT applications. Examples of these applications are presented in [9; 10], respectively, belonging to the areas of Domotics and Electro-mobility with knowledge bases hosting up to one hundred thousand triples. On top of this teaching experience, the authors believe that the learning curve of RDF, RDFS/OWL and SPARQL is often steep, due to the strong linked nature of data. Tarsier should support students learning to deal with RDF knowledge bases by providing an interactive exploration tool for small- or medium-sized knowledge bases (up to a few thousand triples). Through Tarsier, students can play with classes, instances, relationships using filters to toggle their visibility or isolate the interesting entities by moving them on proper semantic planes. The tool would help the students during the so-called \"sensemaking\" activity that consists in understanding the content and overall structure of an ontology [11]. Furthermore, we believe that Tarsier can also be helpful for developers to inspect and debug applications based on Semantic Web knowledge bases. The rest of the paper is organized as follows: Section 2 presents the proposed tool, starting from the initial considerations on the motivations which brought to its conception. Then, its internal software architecture is explained and examined in detail. In Section 3, the proposed approach is shown in practice through examples: several use cases are introduced and commented. In Section 4, an evaluation of Tarsier is proposed based on user surveys and performance analysis. Section 5 summarizes the state of the art of the visualization of semantic KBs, with an overview of the existing tools. Finally, in Section 6, conclusions are drawn and future works are outlined.