I have noticed that both Adobe Bridge and Lightroom write single level lr:hierarchicalSubject tags to XMP files, even though there are no hierarchical keywords involved.
My app doesn't do this and every other app seems to be able to read my XMP files without those tags.
Does anyone know which bit of MWG, DC or other guidelines says anything about this?
I don't recall any standard or guidelines that even take HierarchicalSubject into account. I'd say technically it's a Lightroom tag that's gained acceptance in other programs.
The MWG notes discuss the -xmp-mwg-kw:hierarchicalkeywords tag, which is a structure and harder to read than the plain text -lr-hierarchicalSubject, but the latter contains the same info as the former.
Why I am asking is because some software writes full hierarchies to this tag when only the top and bottom levels contain desired keywords, which then means files containing the middle level get found in searches, even though the specific keyword is not mentioned in the -dc:subject tag
e.g.
hierarchy... Nounours > Didier > Joanna
desired keywords... Nounours, Joanna
result in XMP...
dc-subject... Nounours, Joanna
In order to place Joanna in context, the hierarchy must include the path from top to bottom, but this then means having to write...
lr-hierarchicalSubject... Nounours|Didier|Joanna, Nounours|Didier, Nounours
... which exposes Didier to search engines.
Because there is no chain between Nounours and Joanna, I just write to the -dc:subject tag and ignore any mention of the "incomplete" hierarchy.
But, apparently, Adobe apps include the hierarchy, presumably because it means that only their apps know how to get the correct search results.