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Some thoughts on 'direct access' to XML (long)

  • To: xml-dev@l...
  • Subject: Some thoughts on 'direct access' to XML (long)
  • From: Sean McGrath <sean.mcgrath@p...>
  • Date: Sat, 18 Jan 2003 10:54:07 +0000

wordprocessorml
In the following, the term "BOXED XML" is used to describe the set of
XML technologies exposed to the average programmer by their
tools and vendors of those tools. I.e. XML 1.x, namespaces, XSLT,
W3C XML Schema (and soon) XQuery.

Suggestions:

1. The *only* thing that flows across a wire or between two apps
should be unicode-with-pointy-brackets.  If that is all that is
flowing - and if BOXED XML does not pollute this,
then everyone can be happy.

If, in any given application, the unicode-with-point-brackets is serialized
objects, fine!  If it is process independent semantic business data, fine.
If is some application specific WordProcessorML, fine.
Nobody is forcing anybody to use anything other than
unicode-with-angle-brackets.


2. Object serializations are a very useful and common technique in
programming. Object serialization can be accommodated on top of
unicode-with-angle-brackets without discommoding anyone AS LONG AS BOXED XML
does not shove the object-serialization world-view down everyone's throats.

Those of us who do not wish to treat XML exclusively as a serialization 
notation
for objects are concerned that adding strong data typing, yada, yada into
BOXED XML basically facilitates programmers in thinking of XML as
serialization technology. It isn't, wasn't and shouldn't be allowed to
become a serialization technology.

3. Those of us who are against
xml-as-serialization-notation-for-process-and-platform-specific-objects
tend to worry most about the interoperability and coupling
implications of so doing. Empirical evidence would suggest that you
have to be "of a certain age" to think that this is vitally
important. (It is).

4. What is the easiest way to divide a stock price by
revenue minus expenses? Obviously its something like this:

         Stock = LoadStockFromXML("stock.xml")
         return Stock.price / (Stock.revenues - stock.expenses)

Any attempt at doing that in DOM/SAX/XSLT/XQUery is always going to
come a poor second compared to the native language expression of the
algorithm.

This is a clear case where instantiating a Stock object from the XML is 
*exactly*
the right thing to do. BUT this does not mean that BOXED XML must
provide object serialization/de-serialization.

If you take the shortest route to object serialization, you will just
serialize/de-serialize your objects using whatever XML persistence
tools your environment provides.

If you do that you have - perhaps without realizing it - made your XML 
significantly
less useful. Your XML has become process specific. Change your object
structure (because of requirements changes or bugs) and all your
serializations instantly turn into legacy. Interop with other systems
is no better that it would have been with Java serialized objects,
Python pickles, marshalled CORBA objects etc.

5. Of course it is a good idea that programmers should have tools to
make it easy to read/write XML from their programming language of
choice. However, IT DOES NOT FOLLOW, that BOXED XML must be bent out of
shape to provide strong datatyping, binary encoding and all the other
stuff that typically accompanies notations for object serialisations
and transmission.

Those of use who do not see XML as purely an object serialization
technology worry that this sort of addition runs the risk of
tilting the XML technology stack, away from process independent
unicode-with-angle-brackets. The object world view is so IN YOUR FACE
these days that the warning signs are there for all to see.

6. The right way to serialise/de-serialize objects is on top of, not
inside BOXED XML. And guess what guys? Its not rocket science. I do it
every day of the week. Do I need BOXED XML to natively support that
object-world view to do so? No. Do I want BOXED XML to natively support
that world-view? No!

No because I appreciate that the effort I take to
divorce serialization/de-serialization from my
unicode-with-angle-brackets is well worth it. It repays the effort
over and over and over again as my systems evolve. I can evolve them
without breaking them by applying standard Web techniques of proxying
and interventionist intermediaries. They are a joy to monitor and debug.
I would not sacrifice my unicode-on-the-wire for anything!

7. Programming languages can and should move past SAX/DOM for
accessing XML. For pure document processing, they both have
their place but for Objects and Records (as the terms are used
in mainstream programming), they are sorely lacking. I believe
it is entirely possible to make the programmers life easy
WITHOUT turning BOXED XML into basket of object-serialization
technologies.

This needs to be done ON TOP OF BOXED XML. Otherwise, I fear
that a complete split in the XML world is inevitable.

Don Box recently said that if we insist on looking at Web Services
as an RPC technology we will have missed a glorious opportunity.

No argument there.

I would add that if we insist on viewing XML as an object seralization
technology, we will also have lost a glorious opportunity.

Especially since that two are intimately related.


Sean


http://seanmcgrath.blogspot.com



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