appendix vs. reference?

I'm looking at the docbook 5 documentation. Here's one thing I can't
get my head around.

What's the difference between an appendix tag and a reference tag?
http://www.docbook.org/tdg5/en/html/reference.html
http://www.docbook.org/tdg5/en/html/appendix.html

I have some technical information and tables I wish to put at the end
for the reader's reference. But I'm not sure whether i should do an
appendix or a reference. I plan to have 3 or 4 appendices about
various unrelated topics.

i see that reference has a lot of refentries amd refentries has a a
lot of children, so I understand that reference is probably more
structured. What  kinds of content would be better suited as a
reference instead of an appendix and vice versa?

At what point do you decide an appendix should be a reference?

rj

-- 
Robert Nagle