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Faceted classification and logical division in information retrieval

Library Trends, Wntr, 2004 by Jack Mills

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5.3. Faceted classification of a subject field

This has been the major development in classification for IR in libraries in the past fifty years, although its first formulation was in the work of Ranganathan. Although, curiously enough, Ranganathan never referred explicitly to the fact, the fundamental feature of his Colon Classification is that it divides any given subject in accordance with the rules of logical division. But logical division is not the whole story. The work on BC2, covering every field of knowledge, clearly has shown that the design of a special classification requires recognition of six fundamental steps. These steps must of necessity be taken in the same order, since each step depends on the completion of the previous one. Only the first two use logical division; the other four use extralogical procedures. The steps are easily summarized:

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5.4. The six fundamental steps in design are

* Division of the subject into broad facets (categories) ;

* Division of each facet into specific subfacets (usually called arrays, following Ranganathan) ;

* Deciding the citation order between facets and between arrays;

* Deciding the filing order between facets and between arrays and the order of classes within each array;

* Adding a notation;

* Adding an A/Z index.

5.5. The role of logical division

Before considering each of these steps in detail, the general role of logical division, which governs the crucial first two steps, must be noted. The rules of logical division, developed more than two millennia ago, are admirably brief:

* Only one characteristic of division should be applied at a time;

* Division should not make a leap; steps should be proximate;

* Division should be exhaustive.

The first and crucial rule is purely one of conceptual analysis and doesn't depend on practical considerations. The second and third rules involve to some extent subjective practical considerations as to the size of vocabulary to be accommodated and the degree of specificity with which compound classes are to be described. They are manifested only at the level of arrays (see Section 7). Observance of the first rule is the hallmark of faceted classification; a classification that fails to observe it rigorously throughout the system cannot claim to be fully faceted. The operation of distinguishing the subclasses of a genus has been well-described by Broadfield (1946).

6. DIVISION INTO FACETS

The first step is to assign all the terms constituting the vocabulary of the subject into a limited number of broad categories. The use of the term "category" requires some explanation here. The outcome of the classification is an almost infinite number of possible subject descriptions of documents or parts of documents, nearly all of which will be compound classes--i.e., requiring two or more terms to summarize their content. For example, a document on radiographic diagnosis of bone cancer reflects four different categories of concepts in medicine; if the human body is seen to be the entity with which all medicine is concerned, bone is seen to be a Part, cancer a Process (an action internal to the body), diagnosis an Operation (an action performed on the body), and radiography an Agent of the operation. But the notion of Part is not a category in the traditional sense of the term, since it implies being a part of something--i.e., it is a relation, not a unique and independent category. Similarly, Agent is relative to the action it assists--it is a relation. So facet analysis might be said to be the assignment of terms to true categories (Time, Space, Matter, etc.) and to relational categories (Kind, Part, Agent, etc.).

Faceted classification and logical division in information retrieval

Library Trends, Wntr, 2004 by Jack Mills

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