abstracts

Right now, it looks like the abstracts all start with the same text and
then have a custom sentence or two.  As a reader, I find that awkward
(doing the diff in my head), and I think it short-changes the
differences between the documents.

Let's have each abstract be two paragraphs, where the first paragraph is
shared among all the documents (we can make it a wiki page,
Shared_Abstract and just template-include it) and the second paragraph
is custom for that document.   And the second paragraph should be a few
well-thought-out sentences.   (eg, unlike in XML Serialization where it
is "This document specifies an XML exchange syntax for OWL 1.1."  :-)

      -- Sandro