Claudio Gnoli posted a message to the Faceted Classification group explaining how the Library folks have known (of course!) the concept I discussed recenly of “Nested Facets”. (Bad name!)

“Peter,

something very similar to your idea exists indeed in general bibliographic classifications, both faceted and non-faceted: it is usually called common subdivisions, or common auxiliaries, or even common isolates.

Common subdivisions are not a feature exclusive of FCs, hence a librarian would not call them “facets”. I agree, however, that they are used in a way similar to facets, and maybe can be seen as a first step towards the idea of FC, namely of concept combinability, which was developed later (since 1920s) in library science.

Faceted classification systems, like BC2, have both common subdivisions and facets. The main difference is that facets are limited to a specific discipline — EG “habitat” is only a facet within zoology — while common subdivisions can be applied across disciplines, as in the example above with education and geography.”