SGML vs. XML

[Edward Glowacki]

Quoted from Harold Hunt on Wed, May 16, 2001 at 07:13:02PM -0400:
> Ed,
> 
> >From http://www.oasis-open.org/cover/xml.html:
> 	Valid XML documents are designed to be valid
> 	SGML documents, but XML documents have additional restrictions.
> 
> Essentially, XML is a strict dialect of SGML.  For example, in SGML, and
> therefore HTML, you may define a tag that has an optional closing tag, this
> is not allowed in XML.  In SGML you may have tags that take number or string
> arguments and whether or not to wrap the numbers or strings in quotations is
> tag dependent; for example, in SGML you might have <foo parm1=foo_string
> parm2="foo_string_2" parm3=45 parm4="56">; however, in XML you would have
> <foo parm1="foo_string" parm2="foo_string_2" parm3="45" parm4="56">, notice
> that *every* parameter has quotations around its data.  Tags can be upper or
> lower case in SGML but I cannot remember if case will distinquish two tags
> with the same name; in any case, tags in XML must be all lower case.

Thanks for the clarification... I spent some time searching the
web yesterday looking for a nice clean definition like this, but
even Google is losing some signal to noise ratio on hits... =(

> XML is, in essence, a language processor's language... it is easier to parse
> and process XML because the format of the data is very regular.

Makes sense.

> Currently the XML and SGML DTDs are roughly identical, but in the future the
> SGML DTD will probably be mothballed.

I'm assuming you're still referring to the DocBook DTD, which makes
sense that they'd eventually mothball the SGML version, given what
you've said and what I picked up while searching yesterday.

> You can write SGML according to XML rules in a file that is compiled against
> the DocBook SGML DTD; this is how I write my DocBook currently.  I find that
> writing to the XML rules makes the source much easier to read, and I would
> like to avoid having to tidy up my SGML files when the SGML DTD is
> discontinued.

Interesting idea, just police yourself a bit now and you'll be good
to just say "Parse this as XML now please" and not worry about
fixing anything...

> I'd be glad to answer any other DocBook questions you have.

Heheh, you do realize you just painted a big red bullseye on your
brain, don't you? ;)  

> 
> Harold

-- 
Edward Glowacki				glowack2@msu.edu
GLLUG Peon  				http://www.gllug.org
Imagination is the one weapon in the war against reality.
                -- Jules de Gaultier