[wg11] Part 28 features we could lose

[Ed Barkmeyer]

Lothar Klein wrote:

> I have a maybe naive question:
> 
> Do we really need to use one of these XML format specifications at all?
> Can't we simply provide our own EXPRESS based definition on how to use
> XML-elements and -attributes? - ignoring all these complications from
> those DTD/XML-Schema/RDF?
> 
> As I understand XML only requires that XML documents are well formed -
> we could define what this means for EXPRESS.

Of course we could do this.  But what requirement would it meet?

There are more than a dozen "XML formatting" languages defined, and some 
of them are even standards projects, but XML Schema and WSDL are the 
only two in common use, supported by many tools.  We can easily make 
EXPRESS another unused "XML formatting" language that only a small 
community can read or care about, but who wants to do that?

The presumption of Part 28 is that mapping an EXPRESS schema to an XML 
schema will make the SC4 standard models accessible to the active 
modelers in the "XML schema mainstream".  It will allow the SC4 work to 
be used as the basis for further extension and derivation in many 
industries that don't participate in SC4.  It will allow the SC4 models 
to be understood by programmers educated in XML technologies.  And it 
will allow them, and the corresponding XML documents, to be processable 
by emerging tools in the larger XML community.  None of this can be 
achieved by using a modeling language none of these people can read and 
none of their tools can process.

Why did you write your email in English and not German?  Because most of 
the community you want to influence, and from whose knowledge and 
available resources you wish to profit, does not understand German. 
That is why we translate EXPRESS to XML Schema.

> One argument for this (if it is possible at all) is that all the
> current approaches on mapping EXPRESS-to XML do not provide
> sufficient validation as required by EXPRESS schemas, and what is the
> worth of some "validation" if it is not complete?

Define "complete".  What is the worth of validation if it guarantees 
that the data meets all the constraints of the EXPRESS schema, but the 
data makes no business/engineering sense?  EXPRESS schemas are just a 
further position on the data validation curve, and recent add-ons to XML 
schema are trying to do similar things for XML.  The ontology work is 
beyond EXPRESS in this area, and it will be fitted to XML and XML schema 
in its own way, or perhaps it will be the replacement for XML schema in 
2007, and we will be talking about yet another migration path...

-Ed


-- 
Edward J. Barkmeyer                        Email: edbark at nist.gov
National Institute of Standards & Technology
Manufacturing Systems Integration Division
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