Hierarchy Versus Facets Versus Tags

“The problem of where to file: Is it possible to construct the perfect classification system? A truly first-rate hierarchy would not only have all of the characteristics of FN’s hierarchy, but it would also manage to encode the hierarchy in such a way as to eliminate all ambiguity as to where an item might be found. FN comes pretty close… Nobody builds semantically pure hierarchies, it’s just too much work.”