At this year’s International Semantic Web Conference ISWC 2011, Manchester will be heavily present with 4 papers in the research track, of which 2 focus on justifications.

In the first one, which we presented in similar form at DL, we discuss our user study on the cognitive complexity of OWL justifications. It is quite interesting that, despite the fairly large body of work on explanation for entailments, there have only been few attempts at analysing the effectiveness of explanation approaches with regard to how understandable they are to the average OWL user. Starting with fine-grain justifications (Kalyanpur, Parsia, Cuenca-Grau, DL 2006) which were then defined formally as laconic & precise justifications (Horridge, Parsia, Sattler, ISWC 2008 – won best paper award at the conference), there has been a line of research dealing with making justifications easier to understand by removing superfluous parts (i.e. parts of the axioms in the justification that are not necessary for the entailment to hold). The notion of (non-)laconicity is based on the assumption that superfluous parts distract the user and therefore make it harder to understand why the entailment holds – which, intuitively, seems sound. Moving away from distracting parts only, we want to have a general picture of how easy or difficult justifications are to understand, and why. These ideas are captured in a complexity model (again, Horridge, Parsia, Sattler) which considers certain properties of a justification and the respective entailment, and gives us a score for the cognitive complexity, or hardness of the justification. The considerations behind this model, issues related with cognitive issues, and the validation of the model are discussed in the paper “The Cognitive Complexity of OWL Justifications”, which we’re presenting at ISWC in October.

The second paper is part of my own PhD research and deals with “The justificatory structure of the NCBO BioPortal Ontologies”. Again, this is a topic which has hardly been touched yet by other researchers who deal with explanation in the form of minimal entailing subsets (i.e. MinAs, MUPS  – if for unsatisfiable classes, justifications… maybe we should simply call them MEHs – minimal entailment-having subsets?). While we generally focus on a) finding efficient mechanisms for computing all MEHs, errmm, justifications, or b) analysing the cognitive complexity of individual justifications, there is only a small body of work that looks at multiple justifications. This seems an obvious step, since we know that considering individual justifications for an entailment in isolation does not give us the full picture of why an entailment holds in an ontology. The consequences can be only partial understanding, ineffectual repair attempts, or over-repair (removing or modifying more than necessary). Further, we even know that those multiple justification have relations between them, as they can share axioms, entail each other, be subsets of one another (if we consider justifications for multiple entailments), etc.  To which degree multiple justifications occur in an ontology, and what relations there are between them, can tell us more about the ontology than the simple metrics we see in ontology editors – in the paper I call it ‘making implicit structure explicit’. An analysis of the prevalence of multiple justifications and their relations in a set of BioPortal ontologies is the focus of the paper, which, again, will be turned into a talk at ISWC.

And, in a amusing move, we have had the research track session which contains the two talks named after us: The ISWC organisers decided to call it “MANCHustifications”. You know where you can find us.