Semantic zooming for ontology graph visualizations

Visualizations of ontologies, in particular graph visualizations in the form of node-link diagrams, are often used to support ontology development, exploration, verification, and sensemaking. With growing size and complexity of ontology graph visualizations, their represented information tend to become hard to comprehend due to visual clutter and information overload. We present a new approach of semantic zooming for ontology graph visualizations that abstracts and simplifies the underlying graph structure. It separates the comprised information into three layers with discrete levels of detail. The approach is applied to a force-directed graph layout using the VOWL notation. The mental map is preserved by using smart expanding and ordering of elements in the layout. Navigation and sensemaking are supported by local and global exploration methods, halo visualization, and smooth zooming. The results of a user study confirm an increase in readability, visual clarity, and information clarity of ontology graph visualizations enhanced with our semantic zooming approach.