Libraries have always been aware that knowledge contained in the books of their holdings had to be organized in some way in order to be retrieved again. For this reason, classification systems and subject heading lists have been around for more than 3000 years and have been used and improved throughout history. However, in 1895, two Belgians, Henry LaFontaine and Paul Otlet, also the founders of the UAI, extended a library classification system (the Dewey Decimal Classification) to form a more detailed classification system and contents description of journal articles called the Universal Decimal Classification. In both cases decimal numbers were used to relate to the hierarchical display of classes and concepts. These systems were discipline-based similar to the other systems in the preceding centuries.
In 1933, an Indian mathematician and librarian, S R Ranganatllan, introduced a new form of knowledge organization called the Colon Classification system. Though it was still discipline-based and called a faceted system, it also provided the "building blocks" for compositional expressions of subjects in sentence form. S R Ranganatllan used the colon to symbolize the connection between the subject and the predicate of his classificatory sentences, thus naming his system accordingly.
After World War II, his system and methodology became known in the West, which helped form many faceted classification systems in different fields of knowledge. Even alphabetical descriptor systems, such as the thesauri, were developed in this faceted structure. Concepts organized in facets have the advantage to be accessible in mutually exclusive classes allowing any kind of concept combination according to the requirements of a given case.
It has been defined (FID/CR 1964) that "by classification is meant any method creating relations, generic or other, between individual semantic units, regardless of the degree in hierarchy contained in the systems and of whether those systems would be applied in connection with traditional or more or less mechanized methods of document searching". Indeed, the human capability to make judgements (i.e. formulating sentences in which a subject is related to a predicate) is innate, along with reason, free will and our capability to distinguish between truth and untruth. When human beings make judgments – conscious or not – we are classifying, as the predicates of our judgments relate to a kind of reality which can also be expressed in the form of a concept or a concept class in a classification system.
Thus, whoever wants to organize knowledge needs to create a conceptual representation of the objects of their knowledge and of the activities connected with these objects as well as the properties, conditions, and other relationships occurring with them. In this analytical way the building blocks for knowledge units/concepts are organized. They will then serve to create, in an almost self-organizing way, the necessary order of the objects by bringing together what belongs together, and in the likeness of the functioning of objects in their activities and in interaction with their properties, purposes and their proper environment.
Ordered or organized knowledge thus established should, however, not be looked at as something existing for its own sake. In its externalized form – say in a well-structured faceted classification system – it will become a source for everybody in acquiring, applying, comparing, evaluating, representing and communicating already known or new knowledge (information). It is therefore rather essential for everybody to handle their knowledge carefully and responsibly for their own sake as well as for the sake of others.