Posting to open-bibliography
Cataloging is just one use of bibliographic data. Citations are another important use. While different formats (e.g. Postscript & PDF) should nominally be identical, there’s no guarantee, so I’d argue that each different format should be indexed as a separate manifestation (or equivalent in the schema of your choice).
But this becomes a problem for comprehensibility and means a lot of work. My example was always this page of Thomas a Kempis’ Imitation of Christ:
http://www.ccel.org/ccel/kempis/imitation.html. Is this one “thing” or several? (This site has actually gotten rid of several formats over the years, compare http://web.archive.org/web/20030924082152/http://www.ccel.org/ccel/kempis/imitation.html)
Also, with materials in sites such as the Internet Archive, how do we deal with them:
Is this 8 manifestations? That’s a lot of extra records and work. Is it best for the readers and is it worthwhile to deal with them this way? And what happens when the Archive decides to automatically create, let’s say XML versions for every document. Are these all going to be different manifestations?
For these sorts of reasons, I personally have major theoretical problems with the concept of “manifestation” especially with practical effects when applied generally. I see the “manifestation” primarily as a throwback to the catalog/unit card, and I think there are far better ways of handling them with modern tools.
But I realize we are probably stuck with what we have.