20 most frequent relations in OBO.

The first column states the name of the relation, the second how often the relation is used in any OBO ontology, while the final column indicates occurrence of the relation in formal definitions. We performed the analysis on the full OBO library of ontologies (as of Nov 25, 2010), excluding the NCI Thesaurus, the BFO, the RO, the mappings of OBO ontologies to other ontologies and databases and the logical definitions of OBO ontologies. The full list is available on our project website.