What Does That Number Mean?

I have a vague memory of elementary school librarians explaining how to use the card catalog (remember card catalogs?) and the Dewey Decimal systems.  I recall the unsettling feeling of confusion as I looked at all the tiny numbers and followed the librarian through rows and rows of books while glancing  sideways at my classmates to see if I was the only clueless one ...

Thirty some years later I have discovered that the Dewey Decimal system is not that difficult, in fact it’s really quite clever and very practical.  Here are the cliff notes:  Melville Dewey divided all knowledge  into 10 classes (religion, history, language, etc. ), each class was segmented into 10 divisions and each division dissected into 10 sections.  Therefore, all books can be organized by precise subject and by number.  For instance, a book on butterflies would have the number 595.789 because 500 is natural science, 90 is zoological science, 5 is other invertebrates, .7 is insects, .08 is lepidoptera and .009 is butterflies.  Believe it or not, every new book is assigned a Dewey Decimal number by a division of the Library of Congress (I think this means an actual person!) and then the number  gets approved by OCLC (the Online Computer Library Center) - imagine how the books would stack up if you were out sick for a day or two?  Currently, the DDC is mostly used by public libraries and k-12 schools (about 200,000) in 135 countries but academic libraries have taken up with Dewey’s rival, The Library of Congress Classification.  

The Library of Congress System (LC)  was developed to organize the books in the Library of Congress.  The LC system added classes into its system only when they were needed to add a new book in the Library.  This approach made it easier to add branches for new areas of knowledge (computer science and engineering) and incorporate new subject matter that Melville Dewey never imagined!  The system uses 21 letters of the alphabet for initial classes ( T is for technology, but they don’t all work out that neatly) and each letter has alphabetical subclasses and is then further classified by numbers.  The authors last name and the publication date are added under the LC code and the result is a unique four line name for every book in the library.  The LC system is more efficient  in academic libraries that have larger, comprehensive collections.

And all this time I have just been writing down the number and following the little signs on the shelf.  Tomorrow I will tackle the most interesting thing about either system - Melville Dewey.  He may have been a rockin’ librarian but he was about as eccentric as they come....