A classification is said to have mnemonic value when its notation has the power of “aiding the memory”, i.e. when some of its symbols have more or less the same significance wherever they appear in the schedules or more correctly, when certain aspects are always represented by the same symbols throughout the schedules. Mnemonic devices usually result from a mechanical manipulation of the notational symbols.
The simplest example of mnemonics is that of the common from divisions already mentioned. These divisions can be applied throughout the schemes and once they are committed to memory can be sued and recognized without further reference to the schedules. Note here that it is impossible to regard the Categorical Table of the Subject Classification as wholly mnemonic, since it cannot be said that nearly 1,000 numbers “aid the memory”. Only the most used and popular numbers have mnemonic value.
Another mnemonic manipulation is the use of common Geographical divisions in the main bibliographical schemes. In the Decimal Classification the numbers from the history schedule can be added to main subject numbers to signify “place”. The history number for England is 942, for Germany 943, and under such heads as 655.4, History of publishing and Bookselling, and find the instruction “Divided by countries 930-999”. Thus:
- 655.442 is the History of publishing in England.
- 655.433 is the History of publishing in Germany.
The “9” which signifies “History”, is excluded in the building on these numbers.
Summarizing, a good notation should be:
- Supplementary, i.e. an addition to the schedules.
- Composed of familiar symbols which convey order clearly and automatically.
- Simple, i.e. easy to say, write, type and remember.
- As short as is feasible.
- Flexible, i.e. permitting insertions at any point.
- As mnemonic as possible without interfering with the useful subdivision of topics.