2.2.4. Primary Subject-field Identification

The distinction between a primary subject field and a field of application is another important principle with regard to subject-field classification. The concepts in one area of specialization may be applicable to several disciplines; nevertheless, they belong inherently to one subject field. If your terminology database allows the indication of more than one subject field per terminology record, the primary subject field should be indicated first. (For example, chemistry is the primary subject field of the term chlorine, which designates a specific chemical compound. Its fields of application may belong to industries producing bleaches and cleaning agents, explosives, dyes, drugs, plastics, poisons, and so on. This concept should not be assigned a subject field such as "swimming pools," even if this chemical compound may be used to clean them.)

In a similar vein, it is important to indicate the subject field to which the concept inherently belongs, rather than the subject field of the text in which you may have come across the term.

Related disciplines and convergent technologies may share some knowledge structures, their concepts and the terms that designate them. For instance, computer graphics shares the terminology of shapes and graphics with geometry, and the terminology of data representation with computer science.

Sometimes, the same concept may have different designations depending on the subject field of use, or the same term may designate different concepts in different areas of specialization (for example, flat-top designates an aircraft carrier in military terminology, and a haircut style in barbershop terminology). The indication of the subject field on single-concept terminology records removes any ambiguity for the users consulting the terminology database.

classification systems evolve to reflect progress within a sphere of activity. This progress might entail the appearance of new disciplines, the migration of concepts between disciplines, or the disappearance, merging, or splitting of certain concepts or designations. (For example, bioethics designates a new discipline that combines the concepts of biology and ethics and their respective terminologies, in the study of ethical problems involved in biological research with organ transplantation, genetic engineering, artificial insemination and other reproductive technologies.) Such changes may lead to the indication of more than one subject field on the support on which data related to a single concept are recorded in a terminology database or in a glossary.