8.2 contrib. "Full Disjunction"

I see that a new contrib module was added with the release of 8.2:
http://pgfoundry.org/projects/fulldisjunction/

I found this article that describes the set theory behind it:
http://dbpubs.stanford.edu:8090/pub/showDoc.Fulltext?lang=en&doc=1996-58&format=pdf&compression=&name=1996-58.pdf

Most of it is over my head since I do not have a deep knowledge of set theory as well as all of
the weird squiggly symbols that are used in this paper.

Understanding the concepts of inner, outer, full outer, and cross joins are straight forward to me
as to their application and use. However, since full disjunction is apparently some kind of join:

1) what is its application?
2) how is it used?

Regards,

Richard Broersma Jr.