Colon classification (CC) is a library catalogue system developed by Shiyali Ramamrita Ranganathan.
Many other classification schemes, some of which are unrelated, also use colons and other punctuation to perform various functions.
In CC, facets describe "personality" (the most specific subject), matter, energy, space, and time (PMEST).
These facets are generally associated with every item in a library, and thus form a reasonably universal sorting system.
[2] As an example, the subject "research in the cure of tuberculosis of lungs by x-ray conducted in India in 1950" would be categorized as: Medicine,Lungs;Tuberculosis:Treatment;X-ray:Research.India'1950 This is summarized in a specific call number: L,45;421:6;253:f.44'N5 The colon classification system uses 42 main classes that are combined with other letters, numbers, and marks in a manner resembling the Library of Congress Classification.