User Guide






Ontology Visualization


We used a graph-based approach to represent ontologies in order to make the comparisons and the alignment easier. It is possible to visualize ontologies using several tools dedicated to ontologies (plug-ins for Protege for example) or just RDF visualizers. However, we felt that we needed some visualization tool related to our work and the construction of OL-Graphs from OWL files.

See a more detailed description of OL-Graphs here.

The graph structure makes relationships between language elements
more explicit, e.g., if a class c refers to c' via a
owl:allValuesFrom restriction, a path between the corresponding
nodes in the OL-graph will occur. OL-graphs record further information
that can support comparison, e.g., descriptive knowledge inherited
from nodes of the same or related categories. Finally, to
provide the most complete basis for comparison, one may wish
to bring knowledge encoded in relation types to the object level.
This could be done by adding edges between objects that are reverse,
symmetric or transitive for an existing edge or a pair of edges. Relation types can be handled by saturation of the graph or
in a lazy way: for owl:TransitiveProperty by adding transitivity
arcs; for owl:SymmetricProperty by adding symmetric arcs; for
owl:inverseOf by adding the reverse arcs (both in generic and individual
descriptions); for owl:FunctionnalProperty by adding a
cardinality constraint; owl:InverseFunctionnalProperty is not accounted
for at that stage.

We used the JGraph API and extended it to perform the graph representation of the ontologies.

Below are some examples of visualization.

Ontology1 : See the OWL File - See the visualization result.

Ontology1 : See the OWL File - See the visualization result.

Right now, a layout algorithm still needs to adapted to the representation of ontologies. For example, if you try to visualize the food ontology, many edges will be overlapping and the disposition of nodes on the screen isn't optimized. 



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