Faceted classification and logical division in information retrieval

Library Trends, Wntr, 2004 by Jack Mills

So a particular document entitled "Rehabilitation Following Fracture of the Femoral Neck [in old persons]" would get the index description: Old persons (geriatrics)--Bone--Femur--Neck of femur--Fracture--Therapy-Rehabilitation

Medicine also demonstrates a situation where two fundamental forms of knowledge (here, the natural sciences and technology) may be said to merge in response to the demands of a classification for IR. This situation is sometimes said to be one of the signs that the concept of separate disciplines is breaking down. But nothing is new in this situation; whether we like to think, for example, of biochemistry as being a separate discipline or not, the central conceptual relation between the disciplines of biology and chemistry that meet in the class is clear: it deals with the chemical nature of living things. Chemistry here is a field of action serving the purpose of explaining biological phenomena and as such serves primarily the study of biology. It does not exist as a separate discipline outside the old-established two. Medicine as a technology may be defined as the application of knowledge and skills to produce an artifact of some utility--in this case, a healthier human person. It is inconceivable that the biological bases should not be seen as part of it. Such collocations are at the heart of the notion of helpful order that so appositely defines a main objective in indexing.

7. DIVISION OF A FACET INTO ITS ARRAYS

The classes constituting each facet are now organized into more specific subfacets (called arrays by Ranganathan). At the facet level, classes are undifferentiated and in most cases will not be mutually exclusive. An array consists of mutually exclusive classes. To achieve this condition, which is essential for the retrieval of a specific subject with a minimum of noise, these classes now must be differentiated by applying specific characteristics of division. For example, the primary category in building technology is Buildings, the entity reflecting the end-product or purpose of the technology. These are now differentiated by function (to give residences, etc.), by dominant material (timber buildings, etc.), by number of stories and so on. The classes in the arrays so formed are now mutually exclusive; one cannot have a high-rise single-story building. But in some cases, certain arrays cannot be so easily named. For example, in the large Subject of law facet (substantive law), the first step of division gives three very large subclasses (Private law, Criminal law, Public law), each calling for further subdivision; the array of subclasses of the first includes Conflict of laws, Persons, Obligations, Property, Commercial law--all with numerous subclasses of their own. At this stage, numerous other characteristics still must be applied to distinguish yet more specific arrays; this is clear from the fact that the subclasses are not yet mutually exclusive, e.g., a compound class may be formed for torts of property (in which torts comes from the class Obligations). So the process of subdivision continues until characteristics are so specific that they generate mutually exclusive classes in an array, e.g., Persons by age, Persons by sex.