I have been working on a bug report put in by Jim about the OBO_REL:is_a relation. The label for this relation is not stored in the database because it has its builtin value set to 'true.' The ontology loader simply skips this term at load time. The builtin property is set to true for terms and typedefs such as those from XML Schema Definitions (xsd:Integer is one) and such. Is there any reason why OBO_REL:is_a has to be lumped with these, and not treated differently? Here is the excerpt from the OBO_Relations ontology as hosted on the BerkeleyBOP site

id: OBO_REL:is_a
alt_id: OBO_REL:0000001
name: is_a
builtin: true
def: "For continuants: C is_a C' if and only if: given any c that instantiates C at a time t, c instantiates C' at t. For processes: P is_a P' if and only if: that given any p that instantiates P, then p instantiates P'." [PMID:15892874]
comment: The is_a relationship is considered axiomatic by the obo file format specification. In the representation of obo in OWL, where obo terms are represented as OWL classes, is_a is mapped on to the subClassOf axiom
exact_synonym: "is_subtype_of" []
xref: owl:subClassOf
is_reflexive: true
is_anti_symmetric: true
is_transitive: true