Semantic Web Ontology Map

Sheila Kinsella, Andreas Harth, Uldis Bojars

Here is an interactive visualisation of a part of the Semantic Web as of March 2008. We have created the map based on around 400k RDF files collected from the Web. The map uses SVG and Javascript and consists of two levels: the namespace-level, which gives a broad overview, and the class-level, which gives a more specific view. Each namespace in the namespace-level view has a corresponding class-level view.

Namespace-level:

In the namespace-level map, you can see the most frequently occurring namespaces, denoted using shorthand prefixes. Each namespace is labelled with a count of instances of classes of that namespace. The most frequently connected namespaces are linked with arrows.
To view the count of links between instances of classes of two namespaces, hover over the arrow linking the source namespace to the target namespace.
To view the class-level map for a namespace, click on the name of that namespace.

Class-level:

In a class-level map, you can see the most frequently occuring classes in the corresponding namespace, as well classes from other namespaces which are frequently linked with classes within the namespace. Each class is labelled with a count of instances of that class. The most frequently connected classes are linked with arrows.
To view the count of links between instances of two classes, hover over the arrow linking the source class to the target class. The predicates which most commonly link these classes, and their counts, are also displayed.

Below is the namespace-level view of the Ontology Map, which can be clicked on for the interactive version.

The prefixes used and corresponding namespaces are listed in the legend.

The algorithm works roughly as follows:


 for each type statement:
   increment instance count for class
   increment instance count for namespace of class

 for each triple linking an instance of class A to an instance of class B:
   increment count linking class A to B
   increment count linking namespace of class A to namespace of class B

 generate namespace-level graph 

 for each namespace in namespace-level graph
   generate class-level graph

In order to keep the graphs to a manageable size, we use the following rules to include nodes and edges:

Display at most 20 nodes and 45 links
Display only nodes and links with a count of at least 1000
For class-level graphs: Firstly, choose the most popular classes within the namespace (up to 10). Next, add links to the classes inside or outside the namespace which are most strongly linked to classes within the namespace. Finally, add any other links between classes in the graph.