RE: [xml-dev] What is XML For?

["Mark Seaborne" <MSeaborne@origoservices.com>]

Maybe XML is not convenient for the way you work, if not, don't use it and save yourself a lot of worry.

I work for an organisation which designs messaging standards for the insurance industry in the UK. Where once we would  design EDI (EDIFACT) messages, now we design XML messages. XML is just fine for representing the kind of hierarchical structures that EDI uses. I don't know that it does a better job of it than EDI, but it has the advantage of being ubiquitous.

In one sense XML actually has a big disadvantage over EDI, the same one that is its main advantage, actually. Not many people ever thought of using EDI everywhere, for pretty much everything; it is okay over the wire, but it is normally transformed into something more malleable as quickly as possible, once received. In theory XML is a step up from EDI, because there is a whole raft of tools available to help you to transform it. 

Unfortunately, some organisations appear to be taking the position that because XML is now usable in every tool under the sun, that not only should it be used everywhere, but it can be used everywhere as is. So, at least where I work, I get the distinct impression that organisations are actually wanting the data interchange format to be what they build new back end systems over, so they don't have to do bother with any transformation. This seems an amazingly short-sighted, and dangerous thing to do. A technology touted as an aid to loosely coupling disparate applications, is, ironically, leading to tighter coupling than existed before.

I think this problem is exasperated by organisations such as the one I work for. If you sign up to use a standard within your vertical industry, and send people along to committees to influence message design, you get a false sense of being in control. This will presumably evaporate once member organisations begin exchanging data with organisations outwith the standards body, who refuse to use our standards. That'll learn 'em.

All the best

Mark Seaborne

-----Original Message-----
From: tblanchard@mac.com [mailto:tblanchard@mac.com]
Sent: 24 October 2002 09:59
To: Dare Obasanjo
Cc: Paul Prescod; xml-dev
Subject: Re: [xml-dev] What is XML For?


OK, but I model business process entities using entities and 
relationships.  I animate business process actions using software - 
typically binding behavior to these entities.

XML appears not to be a good match for the kind of data used to 
automate business or represent structure information.  So what's it 
for?  Because its not at all convenient for working with business data. 
  Its too weird.

On Wednesday, October 23, 2002, at 11:44  PM, Dare Obasanjo wrote:

> I completely agree with Paul. I started responding to the original 
> thread until I noticed Paul had already said everything I was going to 
> point out and more.
>
> XML is data, not objects. Understand this for it is the zen of XML.
>
> 	-----Original Message-----
> 	From: Paul Prescod [mailto:paul@prescod.net]
> 	Sent: Wed 10/23/2002 12:32 PM
> 	To: tblanchard@mac.com
> 	Cc: xml-dev
> 	Subject: [xml-dev] What is XML For?
> 	
> 	
>
> 	tblanchard@mac.com wrote:
> 	>
> 	> On Tuesday, October 22, 2002, at 11:15  PM, Paul Prescod wrote:
> 	>
> 	>> No, the structure of the request and the response is generally
> 	>> completely unrelated to the underlying structure of the data 
> store. In
> 	>> fact, the structure of the request and the response is ideally an
> 	>> international standard like SVG, RSS, HRML, ebXML etc. This 
> structure
> 	>> is unrelated to the databases you use to structure it.
> 	>
> 	>
> 	> Can't be true.
> 	>
> 	> The request must name elements in the underlying data store and
> 	> enumerate at least part of the their relationship and optionally 
> specify
> 	> the format of the output. You both expose underlying store 
> structure in
> 	> a request and specify.
> 	>
> 	> SELECT t1.first_name, t1.last_name, t2.country_name FROM t1 user, t2
> 	> locale WHERE t1.locale_code = t2.locale_code;
> 	>
> 	> If I see enough of these queries I can fully deduce the underlying
> 	> structure of the data store.
> 	
> 	You keep talking about queries but I am not. I'm talking about XML. A
> 	_request_ is submitted using either pure HTTP or HTTP+XML. That 
> request
> 	is expressed in terms of business objects, not elements or attributes 
> or
> 	anything to do with the physical representation of the data (either 
> in a
> 	database or on the wire). Here's the canonical (silly) example:
> 	
> 	
> 	-->
> 	<getStockQuote company="MSFT"/>
> 	
> 	<--
> 	<quote>15</quote>
> 	
> 	Now tell me, is there a relational or object database behind that? 
> What
> 	protocol is the server using to keep in contact with the stock 
> exchange?
> 	What do you know other than that there exists a compnay called "MSFT"
> 	that can answer stock quotes.
> 	
> 	(as an aside, I would _never_ do a stock quote that way for a variety 
> of
> 	reasons that are beyond the scope of this discussion)
> 	
> 	 > ...  They are more than related - they are
> 	> tightly coupled.   XSL transformation rules are similar.  I can 
> deduce
> 	> much of the structure of the underlying XML document from the XSL 
> style
> 	> sheet.
> 	
> 	The XML document is a _representation_ of the underlying data. It 
> could
> 	be (and usually is) generated by a Turing complete process. You know
> 	nothing about the underlying data except what the process chooses to
> 	show you.
> 	
> 	 > ...
> 	> Now, if you want to argue that the XML being described is removed 
> from
> 	> the underlying datastore that produced it.  Sure.  Two 
> transformations
> 	> produce some flexibility but any one transformation is brittle with
> 	> respect to the datastore on either side of it.
> 	
> 	Obviously. What's your point? You need an output for a transformation.
> 	An XML document is a very convenient output. A SQL view is a very
> 	inconvenient output. You asked about the difference between SQL and 
> XML
> 	and there's your answer.
> 	
> 	>...
> 	> So you want an interchange format.
> 	
> 	Bingo! That's what XML is.
> 	
> 	> ...  There's nothing wrong with that.
> 	> I'll go so far as to say that a universal object interchange format 
> is a
> 	> good thing.  A way to serialize object networks that is useful for 
> data
> 	> interchange is a good thing.
> 	
> 	You are presuming that people want to interchange objects. But they
> 	don't always (or even usually) want to interchange objects. They want 
> to
> 	interchange data. Some nodes will represent the data as objects. Some
> 	nodes will represent it as lists of list. Some nodes will represent it
> 	as hashtables. That's loose binding.
> 	
> 	> But XML doesn't look anything like what you would get if you were to
> 	> serialize a network of objects.  Its quite different.  Worse, the 
> object
> 	> to XML serialization scheme is open to interpretation in a big way. 
>  (I
> 	> know attributes vs elements is an oldie - and I don't want to 
> respark
> 	> debate). The mapping between XML and say ER models isn't very clean 
> or
> 	> well defined.
> 	
> 	Right again. That's the beauty of it! When I see an XML document I
> 	shouldn't know or care whether the node that produced it was thinking 
> in
> 	terms of ER or objects or lists or hashtables or tuples or ...
> 	
> 	> ...  Too many homegrown ideas running around and the mapping
> 	> problem makes the so-called Object-Database impedance mismatch look
> 	> minor by comparison.
> 	
> 	If you consider impedance mismatches a problem, then yes, XML causes a
> 	huge problem. If you consider them an opportunity to use the best
> 	techniques for a particular job, then XML makes more sense. Relational
> 	databases are kick-ass for holding a kind of information. Objects are
> 	wonderful for in-memory representation of that information. Objects 
> and
> 	relations have an impedance mismatch because they are solving 
> different
> 	problems. XML and objects have an impedance mismatch because they are
> 	solving different problems.
> 	
> 	>...
> 	> This issue has been solved other ways.  Any ER or OO information 
> model
> 	> can be completely described using arbitrary nestings of Maps
> 	> (Dictionaries for Smalltalkers), Lists, and Strings.  If you like 
> you
> 	> can provide a little extra support for automatic coercion for 
> numbers
> 	> and dates.  There is absolutely no piece of information that can't 
> be
> 	> represented with this small set of primitives.  NextSteppers call 
> these
> 	> PLists (property list) and its really easy to rebuild an object/data
> 	> network from a plist.  In fact, its easy to automate.
> 	
> 	Now I know the origin of those horifically silly, dumbed-down data
> 	structures on my Macintosh harddrive. (I got quite a kick out of them)
> 	Anyhow, plists are so 1990s. The modern alternative to XML is YAML. 
> You
> 	should join the mailing list, you'll find many people who feel as you 
> do.
> 	
> 	What are the schema, addressing and transformation languages for 
> plists?
> 	
> 	Also, consider that plists are typically not shared between many
> 	different programs. Is there any plist-vocabulary that has _hundreds 
> of
> 	tools_ around it like XHTML, RSS, SVG or Docbook?
> 	
> 	The more vocabularies are shared, the harder it becomes to extend or
> 	modify them without breaking any particular application. Which is to 
> say
> 	that in the types of applications XML is designed for, there is 
> _almost
> 	always_ an impedance mismatch between the _shared representation_ of 
> the
> 	data and the _in-memory_ representation that any particular 
> application
> 	uses. This is simply because different programmers solve different
> 	problems in different ways!
> 	
> 	Because plists are typically not shared, there is no need for a schema
> 	language for them and seldom an impedence mismatch between them and
> 	their applications. Which is to say, they are not in the same problem
> 	space as XML.
> 	
> 	> I don't see the same thing with XML.  Instead we get the DOM - which
> 	> doesn't look like any other datamodel used to represent information 
> ever
> 	> used in the history of information modeling - oh yeah - except for
> 	> HTML-ish syntax.
> 	
> 	The DOM is an in-memory representation of a serialization format. It 
> is
> 	not the representation your application would typically use at runtime
> 	(unless your application is an XML manipulation tool).
> 	
> 	> ... But HTML was a hack.  Now the hack is enshrined.
> 	
> 	Smalltalk and Nextstep had from 1978 to 1998 to take over the world.
> 	Somehow they failed but XML succeeded. Perhaps you should think 
> through
> 	the reasons for that.
> 	
> 	>...
> 	> No, that would be card image format (line oriented if you like) 
> ascii.
> 	> The next one would be RFC 822 messages.
> 	
> 	Yes, XML could be considered a successor to those standards...of 
> course
> 	it is substantially more powerful in its handling of character sets,
> 	hierarchy and links.
> 	
> 	 >  ...  And XML is not yet universally
> 	> used - its only universally buzzed about.  I have yet to adopt it 
> for
> 	> anything practical at all because I'm still walking around and 
> around it
> 	> saying to myself "what could have possibly lead them to THIS?"
> 	
> 	You'd be hard pressed to find a computer today that does not ship with
> 	an XML parser used pretty close to the operating system level. Plists 
> on
> 	Macintosh. Driver information on modern versions of Windows. Package
> 	maangement on many Linux platforms. etc.
> 	
> 	  Paul Prescod
> 	
> 	
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