Here is a presentation file, please download and try to figure out what it is talking about:

http://www.cs.washington.edu/orgs/student-affairs/gsc/offices/old/433/PoCSi43302/papers/dougz.ppt

I guess you might not able understand, and confused like me, here is the author's presentation:

http://www.youtube.com/watch?v=yL_-1d9OSdk

Enjoy ;->