# Interactive 3D Exploration of RDF Graphs through Semantic Planes
## 3 Use Cases
### Use Case #2: Exploring DBpedia
OPTIONAL{?insdbo:deathPlace?insDeathP ; dbo:deathDate?insDeathD }}. FILTER(?artBirthD > \"1000-01-01\"\"xsd:date) FILTER(?artBirthD < \"2000-01-01\"\"xsd:date) }
```

Using Tarsier, the user is then able to explore the subgraph, as shown in Figure 10.

The subgraph extracted with the CONSTRUCT can be browsed by using the mouse and clicking on spheres and edges to see the relative data. However, where Tarsier comes in help is answering questions through the use of semantic planes. Based on the knowledge base just retrieved, we propose three questions:

1. Are there any relations among influencers? 2. Are there any connections between living artists and influencers? 3. Are there any living artists? **Question 1**: _Are there any relations among influencers? Answering this question is easy through the use of semantic planes. In fact, it is sufficient to create a semantic plane hosting influencers (Step a) and hide unwanted information (Step b), to notice the presence of two links among influencers (Figure 11). Clicking on these links, it is possible to discover that [PERSON] was influenced by [PERSON] and [PERSON] was influenced by [PERSON]. Note that, in Figure 11, all other object properties and all data properties were hidden through the proper controls. Figure 10: Visualization of the graph extracted from DBpedia (Use Case #2), containing all the artists born in Bologna between 1000 AD and 2000 AD and people who inspired them. **Question 2**: _Are there any connections between living artists and influencers?_ An answer to this question can be easily found with two iterative steps that corresponds to the creation of two semantic planes: the first dedicated to influencers, and the second to living artists. This second plane can be created with a simple SPARQL query:

```
PREFIXrdf:<[[http://www.w3.org/1999/02/22-rdf-syntax-ns#](http://www.w3.org/1999/02/22-rdf-syntax-ns#)]([http://www.w3.org/1999/02/22-rdf-syntax-ns#](http://www.w3.org/1999/02/22-rdf-syntax-ns#))> PREFIXdbo:<[[http://dbpedia.org/ontology/](http://dbpedia.org/ontology/)]([http://dbpedia.org/ontology/](http://dbpedia.org/ontology/))> SELECT?art WHERE{?artrdf:typedbo:Artist. FILTERNOTEXISTS{?artdbo:deathPlace?dp}. FILTERNOTEXISTS{?artdbo:deathDate?dd} }
```

A third optional step is to hide unwanted information. These steps and the resulting visualization are depicted in Figure 12. This picture clearly highlights the absence of connections between the two new semantic planes. Thus, at least according to DBpedia, none of the living artists born in Bologna is influenced by another artist. Figure 11: Use Case #2, Question 1: A semantic plane showing the influencers, placed above the semantic plane with the rest of the KB (**a**). Hiding unnecessary edges produces a more effective visualization (**b**). **Question 3**: _Are there any living artists?_ To answer this question, it is sufficient to move all the artists to a dedicated semantic plane and hide all the data properties except dbo:deathDate. These two steps are depicted in Figure 13a,b. All the resources not connected to a green sphere are living artists. The task is then achieved. Figure 13c shows a close-up on the second plane where resources without visible data properties can be considered as living artists. This closer look helps in noticing something strange in the knowledge base. Through Tarsier, in fact, it is easy to notice that many resources have more than one visible green ball, i.e., they died more than once. This is the case, for example, of [PERSON], for which the death date is reported as \"1668-02-08\" and \"'1668-2-8\" (clearly the same date with different formatting) or the case of [PERSON] which instead has two death dates that differ not only for the formatting, but also for the value of the year (\"1641-4-6\" and \"1648-04-06\"). Therefore, Tarsier allowed identifying the wrong use of a functional property. ### Reifacated KBs

The use case presented in this section still involves FOAF with persons and projects.