The number of headings required varies with the work being cataloged. For serials, one to three headings are often sufficient to represent the contents. Go beyond that when there is good reason, for example, assign six headings when cataloging a directory of three academic disciplines as studies in the United States and Canada. Do not assign more than ten headings.

a. Rule of three:

Analogous to the rule of three for descriptive cataloging access points, which limits the number of headings in the same category (personal or corporate) to three, do not assign more than three headings for coequal topics. For example, a statistical report on apple, orange, and banana production would receive headings for those three crops; if pears and grapes were also included, prefer a single, broader heading for "fruit" even though the publication doesn’t cover all fruits. If an intervening level of the hierarchy applies, e.g., "citrus fruit," apply the heading(s) accordingly. The same also holds true for geographic orientation. If a publication covers a topic or situation in more than three places, generalize with a larger geographic area or areas. If that is not possible, consider treating the publication as international in scope and omit place in the heading assignments. Similarly, if the assignment of subdivision is warranted for the social aspects, political aspects, ethical aspects, and financial aspects of the same topic, consider whether the serial covers the topic as a whole and should simply receive a broad heading ([Topic] $x Periodicals).

b. Facility of access:

Facility of access is not always increased or improved by the number of headings provided. It can be as much as a service to the user to assign only one subject heading when it adequately reflects the subject content of the serial. Assignment of numerous, unnecessarily-detailed headings may clutter the results of a more specific search request.

See also:

15.2. Guidelines