RE: Categories and fixed="yes"

[Joe Cheng <Joe.Cheng@xxxxxxxxxxxxx>]

As long as we're on the topic, can we try to get concrete
about solving this for blogs at least? This is main obstacle
to getting a good Blogging Profile spec and I'd really like to
start building some momentum. So I'm just going to start
thinking out loud.

There's the notion of categories that almost every blogging
platform supports (I've taken to calling these
"blog-categories" to distinguish them from the too-generic
concept used in Atom). And there's also tags, which are almost
the same thing. I'm not sure the lines between the two terms
are hard and fast; if anyone can educate me, please do.

Most blogging platforms only support categories, not tags.
Depending on the platform:

* each post can have (zero or one), (exactly one), (zero or
  more), or (one or more) categories assigned
* the list of categories can be opened or fixed
* categories can have distinct IDs (i.e. integer) or can be
  identified solely by their term/label

Some per-platform peculiarities:

* WordPress allows categories to have hierarchy. Terms only
  have to be unique among siblings. Each category has an ID
  (auto-assigned by the server), term, slug, and parent.
  WordPress tags are simply terms (no ID, slug, or parent),
  and behave differently than categories in that clicking
  on them will show posts from not only your blog but
  other blogs as well.
* Roller has two sets of categories: one predefined list that
  is fixed, and one open list. I believe the former is
  defined per server (where the server can have many blogs)
  and the latter is maintained per blog.
* Blogger has "labels" but these are blog-categories as far
  as I can tell.

If there are going to be multiple "schemes" (and you might
consider categories and tags to be two different schemes)
then there needs to be a way to provide a human-readable
label for each scheme.

Given these requirements, can and should the solution be
based on the categories currently defined in RFC5023?
Might one approach be to try to come up with a blank-slate
solution, and once we know exactly what that looks like,
see whether it can be implemented using <categories> without
losing too much?