2005 RO Paper
The origins of RO are with the 2005 paper Relations in Biomedical Ontologies, which defined a core set of relations such as is a and part of.
This ontology was transcribed into an ontology which was originally called OBO_REL. Note that this original version is obsolete, and there are substantial differences with the current RO. For a detailed description see changes to RO since the 2005 paper
RO and BFO
Many relations in RO are generic and can be used in other domains. One idea originally proposed was to cede the core relations to the Basic Formal Ontology (BFO). However, we later decided to retain all relations in RO. Note however that a small handful of RO relations retain a BFO ID space, for example, BFO:0000050 (part of). However, these are in fact part of RO, the IDs have been "donated".
For more details see:
Currently RO is actively maintained by core team with contributions by pull request from many community members. See