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Extracting Modules from Ontologies: Theory and Practice

Cuenca Grau‚ Bernardo‚ Ian Horrocks‚ Yevgeny Kazakov and Ulrike Sattler


The ability to extract meaningful fragments from an ontology is essential for ontology re-use. We propose a definition of a module that guarantees to completely capture the meaning of a given set of terms, i.e., to include all axioms relevant to the meaning of these terms, and study the problem of extracting minimally sized modules. We show that the problem of determining whether a subset of an ontology is a module for a given vocabulary is undecidable even for rather restricted sub-languages of OWL DL. Hence we propose two "approximations", i.e., alternative definitions of modules for a vocabulary that still provide the above guarantee, but that are possibly too strict, and that may thus result in larger modules: the first approximation is semantic and can be checked using existing DL reasoners; the second is syntactic, and can be computed in polynomial time. Finally, we report on an empirical evaluation of our syntactic approximation that demonstrates that the modules we extract are surprisingly small.

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