A faceted classification is a classification scheme used in organizing knowledge into a systematic order. A faceted classification uses semantic categories, either general or subject-specific, that are combined to create the full classification entry. Many library classification systems use a combination of a fixed, enumerative taxonomy of concepts with subordinate facets that further refine the topic. Definition There are two primary types of classification used for information organization: enumerative and faceted. An enumerative classification contains a full set of entries for all concepts. A faceted classification system uses a set of semantically cohesive categories that are combined as needed to create an expression of a concept. In this way, the faceted classification is not limited to already defined concepts. While this makes the classification quite flexible, it also makes the resulting expression of topics complex. To the extent possible, facets represent "clearly defined, mutually exclusive, and collectively exhaustive aspects of a subject. The premise is that any subject or class can be analyzed into its component parts (i.e., its aspects, properties, or characteristics)." Some commonly used general-purpose facets are time, place, and form. There are few purely faceted classifications; the best known of these is the Colon Classification of Shiyali Ramamrita Ranganathan, a general knowledge classification for libraries. Some other faceted classifications are specific to special topics, such as the Art and Architecture Thesaurus and the faceted classification of occupational safety and health topics created by D. J. Foskett for the International Labour Organization. Many library classifications combine the enumerative and faceted classification techniques. The Dewey Decimal Classification, the Library of Congress Classification, and the Universal Decimal Classification all make use of facets at various points in their enumerated classification schedules. The allowed facets vary based on the subject area of the classification. These facets are recorded as tables that represent recurring types of subdivisions within subject areas. There are general facets that can be used wherever appropriate, such as geographic subdivisions of the topic. Other tables are applied only to specific areas of the schedules. Facets can be combined to create a complex subject statement. Daniel Joudrey and Arlene Taylor describe faceted classification using an analogy: “If one thinks of each of the faces of a cut and polished diamond as a facet of the whole, one can picture a classification notation that has small notations standing for subparts of the whole topic, which are pieced together to create