Toward cognitive support for OWL justifications

Justifications are the dominant form of explanation for entailments of OWL ontologies, with popular OWL ontology editors, such as Protégé 4, providing justification-based explanation facilities. A justification is a minimal subset of an ontology which is sufficient for an entailment to hold; they correspond to the premises of a proof. Unlike proofs, however, justifications do not articulate how their axioms support the entailment. We frequently observe that ontology developers find certain justifications difficult to work with; and while in some cases the sources of difficulty are obvious (such as a large number of axioms), we do not have a good general understanding of what makes justifications easy or difficult for ontology users.In this paper, we present an approach to determining the cognitive complexity of justifications for entailments of OWL ontologies. We describe an exploratory study which forms the basis for a cognitive complexity model that predicts the complexity of OWL justifications, and present the results of validating that model via experiments involving OWL users. This is concluded by an investigation into strategies OWL users apply to support them in understanding justifications. Our contributions include an evaluation of the cognitive complexity model, new insights into the complexity of justifications for entailments of OWL ontologies, a significant corpus with novel analyses of justifications suitable for experimentation, and an experimental protocol suitable for model validation and refinement.