A Classification is a system of categories, ordered according to a
pre-determined set of principles and used to organize a set of instances
or entities. This doesn't mean that the principles are always good or
equitable or robust, and indeed, every classification is biased in one
way or another (for example, compare the Library of Congress
classification with the Dewey Decimal System). Classifications are
embodied in every information-intensive activity or application.
Faceted or dimensional classification is especially useful in domains
that don't have a primary hierarchical structure.
Resources can be classified by people, but also by computational processes.