Taken from http://www.kimbly.com/cgi-bin/diamond (link broken):
Welcome to the DiamondWiki. This is an experimental wiki based on the idea of FacetedNavigation. What does that mean, you ask? At the bottom of each page you will see a list of attributes such as "Subject: Wiki" or "Author: Fred". These attributes are used to construct a dynamic directory of all the pages in DiamondWiki. To see the current directory just click on BrowseFacets.
Attributes are similar to tags, but with two key differences. First, attributes are grouped so that, for example, all the "Subject:" attributes are listed together. Second, attributes can be organized hierarchically, allowing users to drill down to see more and more detail.
This is a possibly useful reference for FacetedNavigation, FacetedClassificationInMoin, AutomagicalMenus and SemanticMoin.