While working on the migration mappings for fcrepo3->fcrepo4 properties, I documented all known RELS-EXT and RELS-INT predicates in the Islandora 7.x-1.x code base. The predicates came from two namespaces; fedora and islandora.
The fedora namespace has a published ontology that we use -- relations-external -- and that can be referenced. However, the islandora namespace did not have any published ontologies associated with it.
That said, I have worked over the last couple of weeks with some very helpful folks on drafting initial version of Islandora RELS-EXT and RELS-INT ontologies, and the Islandora Roadmap Committee voted that it should be published. The published version of the RELS-EXT ontology can be viewed here, and the published version of the RELS-INT ontology can be viewed here. In addition, the ontologies were drafted in rdfs, and include a handy rdf2html.xsl to quickly create a publishable html version. This available on GitHub.
What does this all mean?
We have now documented what we have been doing for the last number of years, and we have a referencable version of our ontologies. In addition, this is extremely helpful for referencing and documenting predicates that will be apart of an fcrepo3-fcrepo4 migration.
The initial versions of each ontology have proposed rdfs comments, ranges and and skos *matches for a number of predicates. However, this is by no means complete, and I would love to see some community input/feedback on rdfs comments, ranges, additional skos *matches, or anything else that you think should be included in the RELS-EXT ontology.
How to provide feedback?
I'd like to have everything handled through 'issues' on the GitHub repo. If you comfortable with forking and creating pull requests, by all means do so. If you're more comfortable with replying here, that's works as well. All contributions are welcome! The key thing -- for me at least -- is to have community consensus around our understanding of these documented predicates :-)
I have not licensed the repository yet. I had planned on using the Apache 2.0 License as is done with PCDM, but I'd like your thoughts/opinions on proceeding before I make a LICENSE commit.
I hope I have covered it all. But, if you have have any questions, don't hesitate to ask.