Unification in the Description Logic $\mathcal{EL}$
RTA '09 Proceedings of the 20th International Conference on Rewriting Techniques and Applications
The justificatory structure of the NCBO bioportal ontologies
ISWC'11 Proceedings of the 10th international conference on The semantic web - Volume Part I
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Given the high expressivity of the Web Ontology Language OWL 2, there is a potential for great diversity in the logical content of OWL ontologies. The fact that many naturally occurring entailments of such ontologies have multiple justifications indicates that ontologies often overdetermine their consequences, suggesting a diversity in supporting reasons. On closer inspection, however, we often find that justifications---even for multiple entailments---appear to be structurally similar, suggesting that their multiplicity might be due to diverse material, not formal grounds for an entailment. In this paper, we introduce and explore several equivalence relations over justifications for entailments of OWL ontologies which partition a set of justifications into structurally similar subsets. These equivalence relations range from strict isomorphism to looser notions of similarity, covering justifications which contain different class expressions, or even different numbers of axioms. We present the results of a survey of 78 ontologies from the biomedical domain which shows that OWL ontologies used in practice often contain large numbers of structurally similar justifications. We find that a large justification corpus can be reduced by 97% of its original size to a small core of frequently occurring justification templates.