An essential part of library practice is the separation of the classification system itself and the cataloging of individual documents. A cataloger always assigns the most specific category that is appropriate. Documents are cataloged from a controlled set of terms, then those terms are mapped into a hierarchy which is appropriate for the users.
Libraries commonly make similar local changes to classifications schemes.
He argues that you cannot describe categories in language by sets of properties. It just doesn't work. Instead, categories are built by prototypical examples, and things are included in them by metaphorical extension. These are usually the short nouns in a language, such as house, boat, dog, cat, bush, tree, chair, bed, and so on. The higher and lower levels of hierarchy diverge in different languages.