The Australian and New Zealand Theological Library Association conducts a Virtual Conference in September 2020. In keeping with convention, there is a Pre-Conference Cataloguing Workshop. The Workshop runs uninterrupted for a fortnight on the Association’s e-list, from Thursday the 27th of August to the first morning of the ANZTLA Virtual Conference on Thursday the 10th of September. During Day Two, which looked at the Dewey Decimal Classification scheme, discussion almost inevitably arose about long numbers, the longest Dewey number, and was any of this justified by common sense or common use.
According to The On-Line Encyclopedia of Integer Sequences (OEIS), in 2001 the longest known Dewey Decimal number had 23 digits. Here is the sequence: 3,0,1,1,5,4,3,0,1,2,9,1,7,4,9,2,7,0,5,6,9,4. And here is Bob Kann’s entry in the OEIS: "Staff members at Northwestern University Library Cataloging Department have identified what is believed to be the longest Dewey number ever under serious consideration for assignment: a 23-digit monster for ‘Arab Attitudes Toward Israel’ by Yehoshafat Harkabi, 301.1543012917492705694. The meaning of the number can be broken down as follows: 301-Sociology, 1543-Opinions, attitudes, beliefs on specific topics (Add 001-999); 301-Sociology; 29-Historical and geographical treatment (Add "areas"); 174-Region where specific racial, ethnic, national groups predominate (Add from Table 5); 927-Arabs and Maltese; 0-General relations between two countries (Add "areas"); 5694-Palestine, Israel. In other words: Historical and geographical treatment of opinions on countries where Arabs predominate, and their relations with Israel."
You can read more comment by Bob Kann here: http://www.madisonpubliclibrary.org/all-their-ways
I am thankful to Google for regurgitating an even longer number than Yehoshafat Harkabi’s book. It is registered on a Canadian Blog called ‘Jen in Transition’, dated 2014. “Leave it up to us Canadians to try to be bigger and better!” Jen exclaims, whether in jubilation or irony, or both, is hard to say, before directing us to The Dewey Blog official announcement, https://ddc.typepad.com/025431/2006/02/exciting_tracto.html and I quote:
Remember Classification Club? Everyone at the Manor is a life member, of course. And we're all rejoicing this week, as the news of another unfeasibly lengthy Dewey number continues to filter through the halls. Twenty-one digits? That's nothing. We'll see your "Rednecks in motion pictures" and raise you with a "Buhler Versatile Inc. Strike, Winnipeg, Man., 2000-2001." As every serious student of the Canadian tractor industry will appreciate, the best place for works on this subject is -- deep breath -- 331.892829225209712743090511. That's a whopping twenty-seven digits, and a clear contender for the title of Longest. Dewey. Number. EVER! It's one that we mapped the other day to a new subject heading approved by Library and Archives Canada in December 2005. The base number for strikes in extractive, manufacturing, construction industries and occupations is 331.8928. To this we added the numbers following 6 in 629.2252, which is the number for tractors, then T1—09 + T2—712743 for Winnipeg, and finally T1—090511 for 2000–2009 (as per the instructions at T1—093–099 Treatment by specific continents, countries, localities ...).”
Maybe there should be a contest to create the longest legitimate Dewey number, just to see how far over the edge a classifier can go. Is there an upper limit? Or maybe there should be a cap placed on length, with no number longer than say 40 digits. Would that be helpful or only add to the problem? These flights of whimsy are the logical outcome of striving after over-specificity. Such number games, like 27-digit Dewey numbers, lose sight of the purpose of classification numbers, which is to find the book as easily as possible.
During quiet shelfie moments, as we ponder a line of call numbers in proper order in our library, it becomes apparent that short numbers combined with an effective second element system like the Cutter numbers, are visually the best means to finding the needed book quickly. The longer the number the harder it is to distinguish instantly and the longer it takes to shelve. Both titles mentioned here would be found just as quickly with half or even just a quarter of the suggested numbers. We are grateful for classifiers who, in in-publication and digital records, mark the breaks in the subject make-up of the number, thus giving choice to shorten or lengthen the number.
I suppose that cataloguers are as various as the stars, with long numbers of them psychologically and even emotionally needy for length. Such variables operate completely outside the rigid structures of the Rules, the Rules and their extensions but a means for creative play with infinite elaborations of digits. What I am warning about is the certainty that we have not seen the end of long Dewey numbers, and will live to see a number capable of overturning a Canadian tractor. My own instinct when seeing such enormities is to trust to common sense and take short views.