The question of category versus tag has recently been raised here - with particular reference to the fact that Technorati treats a category as if a tag - a good pragmatic real-life solution that saves all that previous messing about with links rel=”tag” - and whether the distinction should be sharpened.
So what should be a difference between ‘category’ and ‘tag’? If it were a perfect world, with perfect semantics… It’s fairly simple…
A category is an element in a hierarchy - with parents and children. This is the old way, the Open directory method, they know their place, the feudal method maybe.
In contrast, tags are designed to be mixed and matched on an equal basis, search for blog+wordpress+anything and get new and exciting joins. Tags are democracy, social collaboration, del.icio.us, and dare I say, socialism. In posh language, tags create a flat taxonomy.
Boring XML bit
And if and when XHTML 2 arrives, with its proposed navigational lists, (the nl element), it’s foreseeable that one solution might be that the list element label would equal the present usage of ‘category’ and any associated meta would be the ‘tags’.
<nl>
<label>Category</label>
<li href=”http://www.myblog.com/permalink/”>
<meta property=”tags or even dc:tags??”>
comma, separated, tags,
</meta>
Mypost title
</li>
</nl>
And then, presumably, another document to give rules for categories….
It’ll be a whole new semantic ball game when meta can go in the body of an XHTML page - and doesn’t apply to the whole document… even WordPress will be affected.