Hi Feldmahler. Thanks for your response, and I was intending to contact you tonight anyway, but I'll do my best to answer your questions now.
On your first point, technically the tags are just Wiki categories, and will work in the same way as the nationality categories do now, so that adding "Tag=Octets for wind instruments" to the right section of a workpage will add "[[Category:Octets for wind instruments]] to that page. The automatic list of wanted categories will alert the project team to any that are new, or just mistyped
All the tagging will be done by the aforesaid project group (in a similar way to the copyright reviewing), and we won't expect users to try to do this themselves. The biggest task will be to go through all the 20,000+ works already on the site, but that's always something we knew would happen, whatever new system was brought in. This will be done by going through the current genre categories individually, adding the tags and at the same time deleting the old genre/meta-genre references from the page. When the old genre/meta-genre categories are empty, they can be deleted for good.
Once the project starts we also need to make sure that all newly-created pages are correctly tagged as well, which should be a much less arduous task by comparison. Ultimately -- when all the existing pages have been tagged -- the only work involved will be the monitoring of new submissions.
As for the way that the tags group together to form broader categories, I looked at the example of Verdi's Requiem in another thread. Like all tags, the basic structure is the same, i.e. type of work + instrumentation (both terms having strictly defined syntax). So the tag reads: "Requiems for solo voices, chorus and orchestra". All other requiems with the same scoring will have the same tag, and the creation of the tag immediately creates the category of the same name ("Requiems for solo voices, chorus and orchestra"), under which all the works concerned are listed.
The "bottom-up" approach is the novel feature of the system, so rather than start by thinking "how can we break down this large category into smaller and lower levels?", the question will be is "what larger categories does this smaller category belong to?". So, we see that our newly-created category of "Requiems for solo voices, chorus and orchestra" can itself be placed into two larger categories: "Requiems" and "Works for solo voices, chorus and orchestra". Furthermore, the category "Requiems" falls into two the higher-level categories: "Religious music" and "Funeral Music", while "Works for solo voices, chorus and orchestra" is a sub-category of "Choral works".
The connections between the categories are defined when a category is created (using the standard Wiki method of adding "[[Category:xxx]]" to the appropriate page. There is plenty of flexibility for creating new categories at a stroke if the demand exists, simply by combining those at a lower level, and without the need to do any retagging of work pages at all.
Anyway, back to Verdi's Requiem, which by adding the one initial tag of "Requiems for solo voices, chorus and orchestra" can now be found by anyone searching under the following headings:
* Requiems for solo voices, chorus and orchestra
* Works for solo voices, chorus and orchestra
* Choral works
* Religious music
* Funeral music
Some of these "access points" are based on instrumentation, some on the work type, and some on the occasion for performance, which is where all of our previous ideas have stalled. It will require only a minor change to the workpage template, just to allow for the new tags, and at some point the work submission form will need to remove all references to genres and sub-genres.
While the idea is very clear in my head, my typing doesn't always catch up with it, so let me know if you need a better explanation
But if you're satsfied, then I'm currently working on guidelines for the project team, which should be ready in about a week, and a new calendar year seems like a good time make a start. What do you think?