Re: Allocated chapter numbers for specific chapter content

Subject: Re: Allocated chapter numbers for specific chapter content
From: eric -dot- dunn -at- ca -dot- transport -dot- bombardier -dot- com
To: "TECHWR-L" <techwr-l -at- lists -dot- techwr-l -dot- com>
Date: Mon, 20 Sep 2004 17:50:27 -0400

Whoa there!

Sorry Ned, but despite the big words I have difficulty understanding or
believing the difference between SGML and XML.

Ned Bedinger wrote on 09/20/2004 05:15:15 PM:

> SGML was devised as a way to describe a
> document to computers. XML then came
> along as a way to extend SGML's limited
> ability to carry the meaning of a
> document's contents.

Neither SGML not XML are any different in this regard. Neither is more or
less suited to data or content markup. Both are the framework for defining
mark-up languages.

> But first: You are ko-rrect, the SGML
> standard is much bigger than the features
> most users need.

But of course it is. So is the XML standard. Much the same way as all that
could be put into the definition and classifications of automobiles would
be inclusive of vehicles that are far beyond the requirements of the
average user.

> The early set of HTML tags and interpreter
> functions, for example, was derived and
> adapted from SGML (by Tim Berners-Lee, CERN)
> to meet the specialized requirements of
> electronic hypermedia for information
> sharing in the CERN scientific community.

You've got the target right. But it certainly wasn't an "adaptation" of
SGML. HTML is an SGML application.

> SGML was an ISO (International Standards Organization)
> initiative whose time had come.

But, the XML standard is simply a 30 page addendum to the SGML standard.
It essentially limits certain definitions, tightens some rules, and
eliminates others. IIRC, it has more to do with being able to simplify the
restraints for the building of parsers. SGML is very difficult (perhaps
impossible) for a computer to parse if not provided with a DTD. If the XML
standard is followed, a parser should be able to parse any "well formed"
XML structure.

> I think the basic idea behind it was simply
> to go as far as possible in describing the
> meaning of a document's contents in more
> abstract terms, as structure.

SGML and XML are 'meta'languages. They are standards with which to create
markup languages. Whether the resulting markup language structures data,
chemical relationships, mathematical formula, business transaction data,
structures or simply formats content, is complex or flat, is entirely up
to the specific application as defined by the developer.

> SGML has some ability to convey meaning in
> terms of the logical relationships between
> elements of the document. A familiar example
> is the Heading/Subheading hierarchy. SGML
> lets an organization create their own unique
> information structures, and tell them to
> computers.

Which is exactly the same for XML. As is what followed.

> With SGML, information got a new two-way street
> between databases and documents. XML was driven
> by the potential to use even deeper cybernetic
> capabilities to define and process information.
> With SGML you could not distinguish between
> a double-precision number and an apartment
> number, but with XML you can.

Now you've completely lost me. Data in SGML or XML and interpretation of
that data in not dependant in anyway what-so-ever whether the structure is
SGML or XML compliant. It's the parser, business rules, and system used to
process the data that determines the interpretation, storage, display, and

> XML is more closely allied with programming--it
> provides away to tag information in the same terms
> used in traditional low-level programming languages
> and databases. XML amounts to an easier way to
> send computer data in the same stream that carries
> *TML markup information to a web browser.

Well, the concept of "well-formed" has allowed browsers to incorporate XML
parsing into their toolbox. But the rest is marketing fluff. Since the
revival of SGML after being "spiffied-up" by having the XML addendum
added, more development has indeed been accomplished in the world of XML
than the previous years in SGML.

If I'm talking out of the top of my head, please do correct me.

Eric L. Dunn
Senior Technical Writer


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Re: Allocated chapter numbers for specific chapter content: From: Ned Bedinger

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