Based on a reply to this Piwigo forums post, I wrote a blog post, because it may be interesting for more readers.
The “what about managing tags in a hierarchy” question comes back from time to time since 2006 when tags were implemented in Piwigo version 1.6.0. My opinion is that Piwigo already has a very powerful system to manage hierarchies: categories (or albums, which is the new name for categories in the upcoming version 2.2).
The photo organizers listed by bhlevca, ie Lightroom and Digikam, are designed for advanced or professional users and not for sharing purpose. If you take a look at web applications in general, designed for everyday users, you will hardly find hierarchical tags. Yes you will find section/sub-section/sub-sub-section and tag1+tag2+tag3 but not tags places/USA/California/SanFrancisco + animals/mammals/dog.
What makes Piwigo specific and able to use categories to manage hierarchical tags: the ability to associate a photo to several categories while most web applications can only associate an item to a single category and to multiple tags.
OK, so Piwigo doesn’t have hierarchical tags! Fine. What should I do with my hierarchical tags defined in my desktop photo collection managed by Lightroom/Digikam?
Let’s consider you have a photo with the following tags:
I don’t know how these hierarchical tags are stored in IPTC/XMP metadata, but that’s not really the problem. I propose several options:
a) only keep the last level of tag: tags SanFrancisco + dog
b) use each tag level as a tag: tags places + USA + California + SanFrancisco + animals + mammals + dog
c) transform the tag hierarchy into a single tag: tags places:USA:California:SanFrancisco + animals:mammals:dog
d) generate the category hierarchy
I personally really like browsing my photo gallery with tags, so I would consider option b as the most interesting. This way I could see all photos tagged SanFrancisco + animals in just 3 clicks and the photo of this dog in SanFrancisco streets would be in the result set.
Dear reader, please keep in mind that this is an extract from a forum discussion about “how to improve tag management in Piwigo”, none of this options are available in current Piwigo 2.1.