In contrast to numbers for comprehensive works on a subject (see recent blog post), which cover a subject from its various viewpoints within a single discipline, numbers for interdisciplinary works treat a subject from the viewpoint of more than one discipline. For example, works that cover databases from the perspective of both computer science and information science should be classed in 025.04 Information storage and retrieval systems (“Class here . . . interdisciplinary works on databases”); note that the designation of 025.04 as the interdisciplinary number for databases overrides the first-of-two rule, which would call for works equally on databases in computer science (classed at 005.74 Data files and databases) and on databases in information science (classed at 025.04) to be classed in the first of those numbers, i.e., in 005.74. The interdisciplinary works number designation calls instead for the use of 025.04.One restriction on the use of the designated interdisciplinary number for a subject is that the work being classed must include significant material on the subject from the perspective of the discipline of the interdisciplinary number. Consider, for example, a work on symbolism in religion and literature. The interdisciplinary number for symbolism is 302.2223 Symbols (“Class here interdisciplinary works . . . on symbolism”); the comprehensive number for symbolism in religion is 203.7 Symbolism, symbolic objects, sounds (or 246.55 Symbols if predominantly about Christian symbolism), while the comprehensive number for symbolism in literature is 808.8015 Collections displaying symbolism (built from 808.8 Collections of literary texts from more than two literatures, plus facet indicator 0, plus notation T3C—15 Symbolism, allegory, fantasy, myth, as instructed under 808.801–808.803 Collections displaying specific features). (The numbers for Symbolism—literature and Symbolism—religious significance are given in the Relative Index.) The interdisciplinary number for symbolism represents the perspective of social psychology; however, if this perspective is not represented significantly in the work, we do not use the interdisciplinary number for symbolism, but use instead a religion number, as directed by the first-of-two rule.
How can interdisciplinary numbers for subjects be found? As seen in the examples above, interdisciplinary works are sometimes given in class-here notes. But the more general and more useful answer is that they are to be found in the Relative Index. The most efficient strategy for finding interdisciplinary numbers in WebDewey is easily duplicated in the print Relative Index.Interdisciplinary numbers follow the same pattern as other situations in which multiple topics call for the consideration of multiple numbers: Statements here about the number that a work should be classed in should be understood to address only the assignment of the standard DDC number, captured in the 082 field (Dewey Decimal Classification Number) of the MARC bibliographic record. Numbers for the subject from other perspectives that are not chosen as the standard number should be considered for inclusion in the 083 field (Additional Dewey Decimal Classification Number).