The first level of organization was invented by a Greek librarian in the Second Century BC. This is alphabetization -- the idea of organizing words according to the letter with which they begin. If you stop to think about it, this is a fantastic idea. Simple and obvious.
An extension of this idea can be seen in the modern library catalog which is organized not only alphabetically but also in categories:
The best example of this kind of breakdown is a library's actual catalog. Take a look at the catalogs of the ACCD libraries (of which Palo Alto is one) at library.accd.edu. Experiment with various searches and learn more about how it works. (A key to learning any online system, by the way, is READ THE SCREEN. For some reason this is hard for all of us to remember. The instructions are on the screen. So don't forget to read them!)
A more extensive breakdown by category can be seen in the typical encyclopedia. Take out the index to the encyclopedia and observe how subjects are divided and subdivided.
If you wish to read further on this, you may want to jump ahead to library classification systems. However, we shall cover this topic more later.