(Originally posted on the XFML Yahoo! Group.)
The true power of faceted metadata, imho, is that you can triangulate on resources by searching with terms from multiple facets.
Let’s assume I have a thesaurus of communication disorders. One facet might be “Disorders”. By picking a term within Disorders, say ‘Dysphagia’, I can identify resoruces related to that particular disorder. However, what if I was only interested in that disorder as it affects newborn children? I could use an “Age” facet and add the ‘Newborn’ term from that facet to my search criteria. That will then help me narrow further. Let’s add a “Geography” facet and select ‘North America’. Now we have results for ‘Newborns’ in ‘North America’ that have ‘Dysphagia’. This requires accurate indexing of material to be effective.
That is what I think the biggest advantage of faceted metadata rather than just a list of keywords. The Flamenco project is a good example of how it might look in a deployed web site.