Faceted classification and logical division in information retrieval

Library Trends, Wntr, 2004 by Jack Mills

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.).

6.1. Categories in subject fields

All or most of the categories will be found in all or most subject fields. Ranganathan was the first to see the need for initial categories. He provided five and called them Fundamental Categories--Personality, Matter, Energy, Space, Time (widely referred to as PMEST). He claimed that this order represented one of decreasing concreteness; so Colon displayed not only a template for logical division but also a citation order (see Section 8.1). The (British) Classification Research Group (CRG), formed in 1952, developed a more detailed set of categories, entirely consistent with PMEST in outcome but aiming to be more explicit--particularly in its interpretation of Personality; the set may be summarized as Defining system or entity, its Kinds, its Parts, its Materials, its Properties, its Processes, Operations on it, Agents of the Processes and Operations, Place, Time, Forms of presentation (of the information in the documents). The sequence above also embodies a citation order (see Section 8.1).

Assigning terms to categories is a deductive approach to concept organization, and it may be noted that one member of the CRG advocated and developed an inductive approach (Farradane, 1950). This he appropriately called relational analysis, since it is the relations between concepts that are at the heart of retrieval and categories are really a first step in recognizing those relations. Classifications resulting from Farradane's system proved to be remarkably similar to those of faceted classification.

6.2. Facet analysis

The operation of logical division in assigning concepts consists in essence of taking the whole vocabulary of the subject to be classified and asking of each concept, represented by a word or words, what category it belongs to in the context of the subject. This assignment to categories is simply another way of expressing how a particular characteristic of division is applied to obtain classes that share that characteristic, although in different ways (as division of objects by color will produce classes of different colors). The process is best explained by considering some examples of subjects and seeing how it handles every kind of concept.