I’m looking at a recording that is included in a number of box set compilations. For some of these releases, the API attaches relationships via the <relation-list> XML entity. For others, this list does not appear.
Using the web interface, all the releases seem to include relationships (orchestra, conductor, work). Yet for some, the API does not return them. What’s missing?
Here are the specifics. In all releases, we’re talking about track 1 of CD 1, that is, the first track on the release.
This release includes the <relation-list>:
https://musicbrainz.org/ws/2/release/638787d7-f1fb-4f42-b299-0012be2b16d6?inc=artist-credits+labels+recordings+recording-level-rels+work-rels+work-level-rels+artist-rels
These releases do not:
https://musicbrainz.org/ws/2/release/d572e17d-10ef-47f1-bd39-9d1406a252d0?inc=artist-credits+labels+recordings+recording-level-rels+work-rels+work-level-rels+artist-rels
In human-readable terms, the track on the pseudo-release “Haydn Edition (discs 1 - 10)” contains <relation-list>; the tracks on two box sets named “Haydn Edition” do not.
Thanks for any pointers. I’m just starting to learn the API, so I may have missed something obvious.