This pattern describes the minimal number of concepts required to organize a site such that casual visitors find their way while keeping the overhead low.
One of simplest ways of organizing knowledge is categorization. Lump related stuff together. This helps visitors find information faster, since they can search for pages in one category only.
As a casual visitor, all pages seem equally important. How do they find their way around? They need guidance that helps them make meaningful choices.
Navigational aids should require the smallest number of additional mental concepts for visitors to make it easy to understand.
Similarly, for new contributors, we want to keep the barrier-to-entry low. It should not be necessary to know about metadata and site organisation in order to contribute.
Base the site structure on a small number of concepts. Use the plain text page content as the basis.
This is how categorization was used on wikis traditionally. Why not use MetaData for categories? If you are using metadata, you can use it for more fine-grained searches: If you know that categories A is a subcategory of B, then a search for B should also include the search results for A. The drawback is that the search form to use will be more complicated. More power vs. complex searching interface. Do ordinary users really appreciate this kind of trade-off? Does anybody know of empirical evidence? – AlexSchroeder