[DAS2] Progress on XML Schema version of DAS/2.0

[Helt,Gregg]

I'm working on an XML Schema version of the DAS/2.0 schema.  I used the
Trang schema tool to automatically convert the RelaxNG schema to an XSD
doc.  This has provided a good skeleton to start with, but it looks like
there are a number of issues I'll have to fix by hand.  There are many
places where the XSD specifies ordered sequences of elements where there
shouldn't be any ordering restrictions.  Also the way Trang translated
the idea of non-DAS extensions is messy.  And a lot of comments got lost
in translation.  None of these issues look too problematic.  I expect
more problems will come up, but I am making progress.
 
            Gregg