One of the topics of research in my IA class is Ranganathan, the father of Library Science in India. In order to place books in more intuitive locations, with less relying on previously determined constructs, he determined that each book has facets. These are the following:
Personality, Matter, Energy, Space, and Time.
Personality—what the object is primarily “about.” This is considered the “main facet.”
Matter—the material of the object
Energy—the processes or activities that take place in relation to the object
Space—where the object happens or exists
Time—when the object occurs
It then becomes an interesting game to come up with these for each book or even each document file on your hard drive. There is no extremely useful reason for doing this on a small scale, but I suppose if you have a free Sunday and an obsessive need to classify, then you might just give it a try. It’s a fun thing to consider when you are placing pictures into a filing system.