Pathway Commons differs from the other sources as its format, BioPAX, is already represented in OWL. The ''Rules'' column lists the number of SWRL mapping statements used to link each syntactic ontology with the core ontology. For the SBML syntactic ontology, the numbers are combined totals of the imported Systems Biology Ontology and MFO. MFO was used for export only, and therefore its rules are marked with "*'' to show that these are export rules. Statistics generated using Protégé 4 (http://protege.stanford.edu/).