Table 2.

An excerpt of usability issues identified in the Heuristic Evaluation, manually filtered by significance. The issues are ranked according to the average severity assigned by the three evaluators.

Short Title	Description
Interpretation of results	It is very hard to interpret the currently browsed features (see Table 1) of the network visualizations as no information about the actual meaning (or interpretation) of chosen features is provided.
Details of initial concept network visualization unclear	Directly after login - when being confronted with the initial ontology concept network visualization - it is unclear what parts of the ontology are represented as nodes, edges, colors and diameter of the nodes.
Unreadable hover text	When the mouse is hovering over a node in the graphical representation, the hover text is unreadable if the hovered node has many children and parents.
Wrong vocabulary for Audience	Ontology experts might not be familiar with network analysis measures and vocabularies.
Can't move/drag nodes	The network interface should support “drag & drop” for nodes, as there are bigger nodes that sometimes conceal smaller underlying nodes.