Controlled Vocabulary and Subject Headings
The topic of subject headings for categorizing bibliographies came up in the AWOB Blog in November 2010: http://ancientbiblio.wordpress.com/2010/11/09/subject-classification/
The Library of Congress Subject Headings In the US, the Library of Congress Subject Headings are used to classify books by most major university libraries (most of which use Library of Congress call numbers to shelve their books as well.) The classification is fairly robust, and would cover all subject areas this bibliography project is likely to include. It is not easily accessible for free online, however (though it is searchable online at http://id.loc.gov/, this site requires some existing knowledge of how the LCSH work to get results), although most US libraries own a copy of the current edition in print.
L'Annee Philologique Subjects For Classics, the most extensive index, L’Annee Philologique (http://www.annee-philologique.com/aph/ – by subscription), has its own subject classification. This librarian finds it maddening-to-useless, but if you’d like to argue in its favor in the comments to this post I will try to keep my mind open! Upsides: long-standing history of use; downsides: does not cover subjects falling outside the scope of the index, i.e. outside the classical world.
Dyabola Dyabola, the Archäologische Bibliographie of the Deutsches Archaeologisches Institut in Rome (http://www.dyabola.de/, by subscription), also has a structured subject classification (it is most easily viewable as its own entity via the open-access Zenon DAI interface at http://opac.dainst.org/F/M9NIX8X98EYAAD2AV39PEQI1DRGHL357F57SDXRSNBGD5NPVDF-42272?func=option-update-lng&p_con_lng=eng – click on the link labeled “Bibliographical systematic” and it will pop up in a new window). I personally find this to be a fairly useful one for the topics covered in the index. Downside: it is even more limited in scope than L’Annee Philologique, since Dyabola only covers art and archaeology of the Mediterranean.
Suggested in comments by Ashley:
Getty Vocabularies As far as data value standards in art and archaeology, I would recommend using the Getty Vocabularies. These controlled vocabularies/thesauri should allow for more specific control than LCSH. http://www.getty.edu/research/tools/vocabularies/index.html