Designing for faceted search
If you are torn between two places in the taxonomy for a term, consider putting it in both places. That is called polyhierarchy, and it’s a good way to ensure findability from multiple perspectives (although faceted search vendors aren’t too keen on the concept because their tools sometimes don’t handle polyhierarchy terribly well). One caveat: Polyhierarchy is best served within a facet rather than across multiple facets. Since facets should be mutually exclusive, you shouldn’t have much need to repeat terms across facets, which can be more confusing than helpful.
The most important thing, however, is to be prepared to break any of those rules in the name of usability. Essentially, building a faceted taxonomy is more of an art than a science, and it involves understanding your users’ search behaviors.
Faceted search trendsAs the trend toward increased social computing continues, Web 2.0 concepts are entering the realm of faceted search. We are starting to see social tags being used in faceted search and browse interfaces. Buzzillions.com, a product review site, is using social tag-based facets in its navigation, allowing users to refine results based on tags grouped as "Pros" or "Cons."
The site uses a nice blend of free social tagging and control to ensure good user experience; when you type in a tag to add to a product review, type-ahead verifies existing tags and prompts you to select one from the existing list of matches to maximize consistency.
Doing it rightUltimately, search/navigation is one of the main interactions users have with your site, so getting it right is not just a matter of good design, it impacts the bottom line. Faceted search is a very popular and powerful solution when done well; it allows users to deconstruct a large set of results into bite-size pieces and navigate based on what’s important to them. But faceted search by itself is not necessarily going to make your users’ lives easier. You need to understand your users’ mental models (how they seek information), test your assumptions about how they will interpret your terms and categories, and spend time refining your approach.
Faceted search can just add more complexity and frustrate your users if not considered from the user perspective and carefully thought through with sound usability principles in mind. Faceted search is raising the bar in terms of findability. How well you execute will determine whether your site meets the new standard.