Why does OLS not support .obo format?

We have had repeated requests for adding support to OLS for OBO format. OLS uses Jena to parse RDF/XML. Jena has no support for OBO format. As a workaround it has been suggested that the OLS data release pipeline could add a step that converts OBO files to RDF/XML. The problem with this is that the OBO format is underspecified wrt OWL 2 specification. In particular, the OBO format has no way to distinguish between object properties and data properties. This means in the translation from OBO format to RDF/XML (as used by the OWL 2 specification) these differences need to be dealt with on a case-by-case basis. We therefore kindly request that OLS users who still prefer to use OBO format, to convert their ontology to RDF/XML before it is made available for upload to OLS.

Note also that the OBO Foundry define all ontologies using RDF/XML rather than OBO format exactly due to the issues with the OBO format. It is possible that there are some OBO Foundry ontologies that are still in OBO format, but these are all inactive and thus not recommended for use.