Species of Classification:
There are broadly speaking two species of classification systems - enumerative and faceted. Enumerative classification is that in which all classes and their corresponding symbols are enumerated, i.e., listed. It "consists essentially of a single schedule enumerating all subjects of the past, the present and the anticipatable future". In 'other words, the symbols or series of symbols for a, class are available readymade and the classifiers do not, have any. need or authority to construct a number. The Library of Congress Classification System, the Rider's International Classification and the early editions of the Dewey Decimal Classification are examples of an enumerative classification system.
Enumerative classifications are contemptuously described as mark and park systems. "An Almost Enumerative scheme for classification, consists of a large schedule enumerating most of the subjects of the past, the present, and the anticipatable future, and in addition a few schedules of common isolates". Subject Classification of, Brown and Dewey Decimal Classification are good examples.
On the other hand, the other species of classification is known as Faceted classification which consists of schedules of basic classes, common isolates and special isolates only and includes the Almost-Faceted, Rigidly-Faceted and Freely Faceted classification. By definition, "an Almost-Faceted scheme for classification consists of a large schedule enumerating most of the subjects of the past, the present and the anticipatable future; and in addition a few schedules of common isolates and also, some schedules of special isolates". For example; Universal Decimal Classification and Bibliographic Classification of Bliss. In the next type, the "Rigidly-Faceted scheme for, classification, the facets and their sequence, are pre-determined for the entire subject going with a Basic Class". The first three editions of Colon Classification which have given a facet formula for each basic class are good examples of Rigidly-Faceted schemes. But, "in a Freely Faceted Scheme for Classification, there is no rigid, pre-determined Facet Formula for the Compound Subjects going with a Basic Subject". It, essentially is an, Analytico-Sythetic Classification guided by postulates and principles. While, editions 4, 5 and 6 of CC can be described as almost-freely faceted schemes for classification, edition 7 of CC can be considered as a fully freely faceted scheme for classification.