What is XML for?

Simon St.Laurent simonstl at simonstl.com
Fri Jan 29 18:46:48 GMT 1999

At 11:50 AM 1/29/99 -0600, Paul Prescod wrote:
>I've noticed a very unfortunate trend among my customers. They want to
>replace relational databases with XML. They want to replace purpose-built
>query languages with XSL. They want to replace object models and UML with
>DTDs and "XML Schemas". People are also talking about using the DOM as the
>interface to data of all sorts. This trend is very worrisome and will
>likely lead to a backlash against XML.

I've noticed a very unfortunate trend among certain members of the XML
community. Whenever someone proposes using XML in any way that goes beyond
interchange and documents, they become very concerned that the system
proposed won't work and that the sky will fall in on XML.  They see
backlash lurking in every corner, with hordes of journalists waiting for
XML to collapse so they can proclaim it the next OS/2. (Apologies to any
diehard OS/2 folks out there.)

XML is many things to many people.  It is simple enough and generic enough
that if you try hard enough, you can stretch it to fit just about any
problem in computing. It may not always be the optimal approach, but it
fits many problems very well.

XML is not just a file format any more, or an interchange format.  XML
describes a set of structures that are extremely generic, and which map
very well to a wide variety of structures used in data processing.  Some
people look at an XML document and see the markup; others see the
structures; others see a transformation of those structures, into program
data, a program, or nicely formatted programs for an opera.  XML has, in
many ways, left behind its roots as a document format and become something
else, a generic set of tools for manipulating information.  

Tools that work for XML will work on data across an enormous number of
domains, and if those tools follow similarly generic standards, they may
even work across implementations from an enormous number of vendors using
very different technology.  I don't feel that we've achieved nirvana, but
for the first time we may actually have an opportunity to genuinely move
toward interoperable computing without having to all be using the same
languages and platforms, and that's a big step.

Why does XML have an opportunity, when SGML had the same tools and more?
Because it's simple enough for neophytes to walk up to and explore, and
because processing it isn't very hard.  Two good things that lower the cost
of development significantly.

>I'm working in the opposite direction. I wonder: 
> * Isn't OQL pretty close to an XML query language?
> * Aren't STEP and ODL pretty close to being XML object model schema
> * Wouldn't it be nice to have more formal mechanisms for characterizing
>languages (like XQL, XPointer, URLs, JavaScript) that do NOT use
>angle-bracket syntax?

You can wander back into the woods if you like, but don't expect everyone
to follow you. Heading back to implementation-specific standards is
necessary for some applications, but it isn't going to work across the

Your last point about formal mechanisms is worth considering, though I'm
not sure it's 'the opposite direction' at all.

>Another worrisome trend is that people creating the XML standards would
>rather invent rather than learn about things that already exist.
>"NI at theW3C" syndrome?

What, like XSL?  Building a whole new formatting vocabulary when CSS
already exists?  I suppose.  The W3C does have the key responsibility of
building things _for the Web_, and if that happens to spill over into other
fields, great.  But I'd rather see the W3C invent something new that works
on the Web than leave us with older tools that don't work well on the Web.
I'd like to see the W3C open its process a lot more, but apart from that I
don't have too many problems with their mandate.

What's XML for?  Anything you like.  Build it, and see if people come.

Simon St.Laurent
XML: A Primer / Building XML Applications (March)
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