Section 5.7 of the DDC Introduction addresses how to classify a work that includes more than one subject in the same discipline:
5.7 A work may include multiple subjects treated separately or in relation to one another from the viewpoint of a single discipline. Use the following guidelines in determining the best placement for the work:
(A) Class a work dealing with interrelated subjects with the subject that is being acted upon. This is called the rule of application, and takes precedence over any other rule. For instance, class an analytical work dealing with Shakespeare's influence on Keats with Keats. Similarly, class a work on the influence of the Great Depression on 20th century American art with American art.
Here is introduced the rule of application, a rule that guides the classifier in classifying a work on interrelated subjects in which one subject can be said to act upon the other. The rule states that such a work should be classed with the subject acted upon. (The characterization of the rule of application in the Glossary—"The rule instructing that works about the application of one subject to a second subject or the influence of one subject on another subject are classified with the second subject"—indicates that the single discipline context in which the rule of application is presented in the Introduction is not defining/restrictive.) The Introduction also makes clear that, if multiple rules apply to the classification of a work and one of those rules is the rule of application, it "trumps" (takes precedence over) all other rules. (In fact, the pre-eminence of the rule of application is the motivation for starting our review of the rules here.)The rule of application is also mentioned in section 8.12 of the Introduction, where we learn that the table of preference at the beginning of Table 1 is overruled by ("yields to") the rule of application. For example, "by the rule of application, teaching financial management in hospital administration is classed in 362.110681, not 362.11071, even though notation 07 is above notation 068 in the table of preference." We have three subjects here: hospitals, financial management, and teaching. Teaching is applied to financial management, while financial management is applied to hospitals, financial management constituting one aspect of hospital administration. Since hospitals are the core subject acted upon, we start with 362.11 Hospitals and related institutions. We then add standard subdivision T1—0681 Organization and financial management because this is the subject element that acts upon hospitals.
Perhaps the most common applications of the rule of application concern the philosophy of a subject or the history of a subject. Such works are classed in the subject, with standard subdivisions T1—01 Philosophy and theory or T1—09 History, geographic treatment, biography added to express philosophy or history, respectively. Thus we have 109 for the history of philosophy and 901 for the philosophy of history. (Imagine if the rule of application were reversed and the philosophy of all subjects was to be classed in the 100s and the history of all subjects in the 900s!)
Given the rule of application:
- Works on Shakespeare's influence on Keats are classed in the number for Keats (821.7 English poetry—1800–1837) rather than in the number for Shakespeare (822.33 William Shakespeare under 822.3 Drama of Elizabethan period, 1558–1625).
- Works on the use of data mining to support business decisions are classed within business, in a subdivision of 658.4038 Information management ("Class here gathering of information by management or use in managerial decision making; information resources, knowledge management") rather than in 006.312 Data mining, its interdisciplinary home within computer science. The specific number for data mining to support business decisions is 658.403802856312, built with the base number 658.4038, plus T1—0285 Computer applications, plus the numbers following 00 in 006.312, following the add instruction at T1—0285.
- Works on the chemistry of hydrocarbon combustion are classed in the number for hydrocarbons (547.01 Hydrocarbons) rather than in the number for combustion (541.361 Combustion). Numbers for specific kinds of compounds identified by component elements allow for addition from the internal add table under 547, where we find 0453–0458 Specific topics of physical chemistry and the add instruction to add to 045 the numbers following 541.3 in 541.33–541.38. The specific number for the chemistry of hydrocarbon combustion therefore is 547.0104561.
- Works on the fractography of glass are classed in the materials science number for glass (620.144 Glass) rather than in the number for fractography (620.1126 Resistance to fracture (Fracture mechanics)). Numbers for specific kinds of materials allow for addition from the internal add table under 620.16–620.19, where we find 1–9 Specific properties and nondestructive testing and the add instruction to add the numbers following 620.112 in 620.1121–620.1129. The specific number for fractography of glass therefore is 620.1446.
- Works on obedience training for retrievers are classed in the number for retrievers (636.7527 Retrievers) rather than in the number for obedience training (636.0887 Pets ["Class here obedience training"). Numbers for specific breeds of dogs allow for addition of notation from the internal add table under 636.1–636.8, where we find 35 Training. The specific number for obedience training for retrievers therefore is 636.752735. (The decision to class obedience training for retrievers with retrievers rather than with obedience training is reinforced by the rule of zero, which we will look at later.)
It is not by accident or mere coincidence in the final three examples that provision has been made for building numbers that express the complex subject we were interested in representing. These reflect a pattern common throughout the DDC in which the rule of application has, in effect, been built into the DDC. A follow-up post will give further examples of where the rule of application is woven into the schedules.