Re: candidate keys in abstract parent relations

> Could you, perhaps, define the primary key as the catalogue number, title,
> release date, and record label together? If that isn't sufficient to handle
> all possible permutations, then surely there has got to be another piece of
> data that could be lumped in with the primary key. The country of release as
> well, maybe.

If you read my original posting, you'll see that that strategy works fine for Releases, but not for Albums. An Album is a collection of Tracks with a name, which can be released as part of one or more Releases. Almost all of the attributes you enumerate (Label, Label catalog number, Locale, Locale-specific title, release date) are defined on the Release, not the Album. In the domain I'm modeling, labels release the same collection of songs at different times with different cover art in different countries, and they also release totally different collections of songs at the same time with the same name (think about albums that are bundled with "bonus CDs").

My model includes several characteristics that are somewhat idiosyncratic, but that I feel model the way that music collectors think about music better than less general methods:

1. an album bundled with a bonus CD is a different version of the same album, when the bonus CD contains material thematically linked to the first CD (in 1993, Slowdive released two versions of their album _Souvlaki_, the first being a single CD, the second containing a second CD compiling most of their early EP releases).
2. I think it's incorrect, as well as imprecise, to disambiguate two collections of tracks via their title when the disambiguating information is nowhere visible on the album's packaging. I have the original version of The Cure's "Faith" on CD, as well as the 2005 remaster, which includes roughly three times as much music as the original release. In iTunes, I have them both ripped, with one called "Faith", and the other called "Faith [2005 remaster]". I *could* make this a convention and require Album(primary performer, title) to be unique, but that's a somewhat peculiar convention.