From what I've seen, the ID element does not have to be UUIDs. One way to handle this is to add a new column (`uuid` or whatever) when the repo and build objects are created, but I don't think it is wise at this time. (The cost of migration far outweighs the benefits we seek.)

For this, then, we might be able to get away with something much simpler--say `travis_repo:repo_id` and `travis_repo:repo_id:build_id`.