Source of the files:

so.obo: https://github.com/The-Sequence-Ontology/SO-Ontologies/blob/master/releases/so-xp.owl/so-xp-simple.obo
so-xp.obo: https://github.com/The-Sequence-Ontology/SO-Ontologies/blob/master/releases/so-xp.owl/so-xp.obo
sofa.obo: https://github.com/The-Sequence-Ontology/SO-Ontologies/blob/master/releases/so-xp.owl/subsets/SOFA.obo

Current HEAD is 6f8dfd4aebd4427baad07535b6250f4622b1b075
