Recently we received a query: the notes at 641.22 and 663.2 are exactly the same, so which number is actually the comprehensive number for wine?
Here are the notes:
641.22 Wine
Class here grape wine, comprehensive works on white and red wine, comprehensive works on specific white and red wines (specific brands, estate wines)
663.2 Wine
Class here grape wine, comprehensive works on white and red wine, comprehensive works on specific white and red wines (specific brands, estate wines)
First, we need to distinguish between a comprehensive number and an interdisciplinary number. There can be more than one comprehensive number for a topic, but only one interdisciplinary number. Here are definitions from the Dewey Decimal Classification glossary.
Comprehensive number
A number (often identified by a "Class here comprehensive works" note) that covers all the components of the subject treated within that discipline. The components may be in a span of consecutive numbers or distributed throughout the schedule or table.
Interdisciplinary number
A number (often identified by a "Class here interdisciplinary works" note) to be used for works covering a subject from the perspective of more than one discipline, including the discipline where the interdisciplinary number is located, e.g., the interdisciplinary number for marriage is 306.81 in Sociology.
The comprehensive home-economics number for wine is 641.22. A subdivided entry in the Relative Index shows the discipline:
Wine—home economics 641.22
The comprehensive commercial-processing number for wine is 663.2. A subdivided entry in the Relative Index shows the discipline:
Wine—commercial processing 663.2
Thus both 641.22 and 663.2 are comprehensive numbers for wine.
Then what is the interdisciplinary number for wine? The quickest way to find out is to browse the Relative Index. Under "wine" we find multiple entries—but only one unsubdivided entry:
Wine 641.22
That unsubdivided Relative Index entry signals that the interdisciplinary number for wine is 641.22.
Another approach that works in this case—though not in all cases—is to look for notes in the upward hierarchy.
At 641.2 Beverages (Drinks) is the note:
Class here interdisciplinary works on beverages
That note has hierarchical force:
Hierarchical force
The principle that the attributes of a class as defined in the heading and in certain basic notes apply to all the subdivisions of the class and to all other classes to which reference is made.
At 663 Beverage technology is the note:
Class interdisciplinary works on beverages in 641.2
That note also has hierarchical force.
We call this last approach reading up the hierarchy so you can find the notes above that have hierarchical force—notes that drip down.
An example of an interdisciplinary work classed in 641.22 is The New York Times Book of Wine: More than 30 Years of Vintage Writing.
An example of a work that focuses on commercial processing of wine classed in 663.2 is Concepts in Wine Technology: Small Winery Operations.
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