Hierarchies, trees, paradigms, and facets

How to Make a Faceted Classification and Put It On the Web: "Kwasnick (1999) identifies four classificatory structures: hierarchies, trees, paradigms, and facets. When one of the first three works, use it. If some other organizing principle, such as a timeline or ordering by size, works, use it. The design of the classification must follow its purpose, and different things can be classified in different ways for different purposes, requiring different structures. If the others are insufficient, look to facets."