Right now, support for box sets is very poor. The best we can do is to collapse the release into one long list of discs, which sorta works, but results in large unmanageable releases which aren't an entirely accurate representation of the release because quite a bit of information is missing.

Box sets are typically releases which contain releases. That means that while the box set has a catalogue number, barcode and packaging, so do the releases which make up the box set.

Often, these releases are identical to the separately released versions (including the same catalogue number and barcode), but we have no way of including that release (since they're identical, any changes to that release should also apply to the one in the box set). Instead we have to duplicate the data and lose the catno/barcode in the process.

We could in theory add all of the catalogue numbers to the release, but that's confusing because we don't know which one belongs to the release itself and which to the individual releases. Medium catalogue numbers (MBS-1735) would be an improvement but would still have problems - an individual release with multiple discs would be treated as two separate mediums which happen to have the same catalogue number, when really it's the catalogue number for the release which the mediums are a part of. It also gets confusing when an individual release has a catalogue number and its discs also have catalogue numbers - we basically end up with the same problem for box sets that medium catalogue numbers wants to solve for normal releases.

Another problem is that individual releases in a box set can contain multiple discs, but we have no way to group those discs together.

Disc titles are also a problem. We're already using the disc title for the release titles, so we have to squish both pieces of information into the same field.

A release I have which demonstrates most of these problems is http://musicbrainz.org/release/bd248422-cce0-45a6-b4e7-077f5874c15a This "7×CD + VCD" release is really just these five releases (same barcodes and catalogue numbers) in a box:

• http://musicbrainz.org/release/1f4c4892-2039-4545-9658-5f15248c7861
• http://musicbrainz.org/release/800a08fd-8e63-4007-8c77-1956f3bd7779
• http://musicbrainz.org/release/8138b672-50ad-4604-b3f2-188e3731df93
• http://musicbrainz.org/release/787ad2d2-3e79-499d-9cab-4521b9401c53
• http://musicbrainz.org/release/a99aadd7-a3f2-35b5-82fb-b421feebfb26

I've been thinking for a while about how we could solve it. The best thing I've thought of so far is to have a way to mark a release as a box set (release group type maybe) and for box set releases to have no mediums. Instead, they would be linked to the individual releases which make up the box set. This could be done via relationships if we add ordering to relationships, or it could be done via a special table in the database. Then when displaying a box set release, we would embed the individual releases (preferably collapsed by default).

One problem with that is how to deal with discs which are only available within a box set. The method I suggested would require them to exist as separate releases in the database even if they weren't originally released that way. This may or may not be seen as a problem (one advantage is that it's closer to how people see these releases - people often want to tag each release in a box set as a separate release and I've seen people split up box sets and sell them separately on numerous occasions)

See http://musicbrainz.1054305.n4.nabble.com/Adding-releases-without-adding-their-track-lists-td4456385.html#a4481826 too.