Relational patterns in OWL and their application to OBO

Directed acyclic graphs are commonly used to represent on-tologies in the biomedical domain. They provide an intuitive means toformalize relations that hold between ontological categories. However,their semantics is usually not explicit. We provide a semantics for a partof the OBO Flatfile Format by extending OWL with a method to expressrelational patterns. These patterns are OWL axioms with variables forclasses. The variables can only be filled with named classes. Addition-ally, we provide a semantics for open patterns in OWL. Our method isapplicable to the OBO Flatfile Format, and provides a means to designOWL ontologies using complex ontology design patterns. Therefore, itleads not only to an integration of the OBO Flatfile Format and OWL,but extends OWL with an intuitive interface for designing ontologies us-ing complex definition patterns. A prototypic implementation and testresults are available at http://bioonto.de/obo2owl.