Clarification on XML Concepts

[Graham Tillotson <Graham -at- MEGSINET -dot- NET>]

The discussion of SGML/XML/HTML needs some clarification. In the world
of markup languages, XML exists as a subset of SGML, and these two
languages are significantly different than HTML.

Think of XML as you would a database: you start with a DTD (Document
Definition Type) that specifies what can go into a specific type of XML
document. If you wanted to create a document called PLAY, you would use
precise syntax to say that each PLAY is comprised of one or more ACTS,
and each ACT can have one or more SCENES. You have PLAYERS, and they can
have DIALOGUES. This is the same way you would setup database
tables--the usual entity and attribute routine. An XML document should
be structured in conjunction with a DTD, and once you have a well-formed
document, then you can bring in XSL, the related style language, to
control the format of the output. XML is "extensible" because I can make
up whatever document type I want, from a Procedures Manual to a Bedtime
Story, and I am not limited to a static set of HTML tags.

Mary Deaton said:
"Depending on which DDT you push the data into, it is formatted
differently. As sub-sets of SGML, HTML and XML can be used in somewhat
the same ways, although they are optimized for online delivery."

I think that this explanation may be misleading. If by "DDT" she means
DTD, then the process is somewhat reversed. You would never "push" an
XML document into a DTD; rather, the XML document is based on a DTD that
you setup first. When a browser like IE5 looks at an XML page, it uses
the DTD as a reference to parse out the elements.

And, (just like with a database), XML content is no more "optimized" for
online delivery than information in database tables is "optimized" for
use in forms and reports. XML content, like database content, is
optimized as DATA so that you can control it. You are free to use your
imagination as to how the content will be delivered.

I would caution against lumping XML and HTML together, because although
they work together (you don't have one without the other) they are much
different CONCEPTUALLY. Having logged long hours doing database
development, I see documentation experts facing the same challenge that
confronts those who are new to relational design--how to mentally
separate content from formatting. This is exactly what XML does, because
it lets you separate content from HTML formatting. Not an easy concept
to grasp, I admit, but on essential to future document development in a
web environment.

Graham Tillotson


 From ??? -at- ??? Sun Jan 00 00:00:00 0000=