Re: W3C Schema website intro

Gary Robertson writes:

>> I wrongly assumed, as I'm sure 
>> that most people 
>> would, that this meant 

>> "They provide a means of FULLY defining the 
>> structure, content and semantics of ALL 
>> XML documents". 
 
>> and planned a project based on this 
>> assumption, thus involving my employer 
>> in a lot of fruitless expenditure and me in 
>> a lot of mental anguish. I think this is a reasonable 
>> suggestion. Note, however, that the third paragraph of the 
>> schema structures specification contains the warning [1]:

"However, the language defined by this specification does not attempt to 
provide all the facilities that might be needed by any application. Some 
applications may require constraint capabilities not expressible in this 
language, and so may need to perform their own additional validations."

It's pretty much right up front, before you get to the heavy duty 
technical stuff. 

Also, doing really full validation is pretty much impossible if you're not 
the application.  Yes, a Turing complete programming language can check 
many things, but being less declarative it has its own problems;  we chose 
a declarative language.  Even then:  it's easy to create schema language 
that will do some checking on whether a certain field resembles a credit 
card number;  if you're not the application, it's nearly impossible to 
tell whether the card is stolen or whether the number was never issued 
(both examples of being "invalid" for the application's purposes).

In practice, no schema langauge can do more than adopt one tradeoff or 
another in deciding what to model and validate.

[1] http://www.w3.org/TR/xmlschema-1/#intro-purpose

------------------------------------------------------------------------
Noah Mendelsohn                                    Voice: 1-617-693-4036
Lotus Development Corp.                            Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
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"Gary Robertson" <gazinyork@hotmail.com>
Sent by: xmlschema-dev-request@w3.org
12/03/01 02:36 PM
Please respond to "Gary Robertson"

 
        To:     <xmlschema-dev@w3.org>
        cc:     (bcc: Noah Mendelsohn/CAM/Lotus)
        Subject:        W3C Schema website intro


I wonder if it would be helpful to newcomers 
if the introduction to the W3C Schema website
were modified to explain the scope of W3C 
schema capabilities. For example, at the moment 
it is stated that: 

"They provide a means of defining the structure, 
content and semantics of XML documents".

I wrongly assumed, as I'm sure that most people 
would, that this meant 

"They provide a means of FULLY defining the structure, 
content and semantics of ALL XML documents". 
 
and planned a project based on this assumption, 
thus involving my employer in a lot of fruitless 
expenditure and me in a lot of mental anguish.

The statement could be rewritten more precisely
in several ways:


"They provide a means of defining the structure, 
content and semantics of SOME XML documents". 

or 

"They provide a means of PARTLY defining the 
structure, content and semantics of XML documents". 

or

"They provide a means of defining the structure, 
content and semantics of those XML documents whose 
structure, content and semantics they are able to define."

which is my personal favourite as it combines accuracy, 
circularity and the appropriate academic tone ;-)

Seriously though, this kind of statement is in danger 
of causing an Emperor's new clothes phenomenon 
which can only do damage to the W3C's reputation.

--
Gaz

Received on Monday, 3 December 2001 15:57:18 UTC