I think you can get away with your categories, or iTunes, if you recognize that a single item needs to be listed in more than one hierarchy. Technically, a leaf node can exist at the end of any number of branches. So, a Ruby conference presentation (Technical) on how a startup formed and succeeded (Business) at a cool new web site that allows musicians to get together for charitable social causes (Music, Society) ought to be found at the end of which ever of the paths a browsing visitor travels down.

Note that logically, if an item can appear at the end of any number of branches, you don’t have a tree structure, but a web. And you haven’t created a taxonomic hierarchy as much as a tagged web. Which is a Good Thing.

Trying to reduce the scope of human activity to 15 categories is an exercise in frustration. I would argue for a more flexible, two-tier system.

If you arbitrarily limit the number of categories to an integer based on screen real estate, you will wind up with blandly generic categories, and a lot of items that have be put in “Other” or “Miscellaneous.” You will also have to put many items in two or more categories. In either case you will still have to look at the tags to get a better sense of the actual subject matter of the content.

Better, I think, to have a smaller number of extremely generic categories (Business, Politics, Technology, etc) with an easily expandable list of subcategories that can be responsive to changes in the ongoing cultural conversation.

If you do this with rollovers and flyout submenus, it will actually take less screen real estate. Then make sure the database allows for assignment to multiple categories and subcategories.

:: SH

we use “ideas” at earideas.com … useful for, well, this kind of content:
http://earideas.com/earideas/explore/feeds/Ideas

(and many feeds are assigned 2 cats, eg. “ideas” and “technology”)