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RE: dynamically generated XML Schema?! Re: R: [xml-d


use case schema


> -----Original Message-----
> From: Chiusano Joseph [mailto:chiusano_joseph@b...] 
> Sent: Wednesday, November 03, 2004 09:28
> To: Burak Emir; Michael Kay
> Cc: Chizzolini Stefano; xml-dev@l...
> Subject: RE:  dynamically generated XML Schema?! Re: 
>  R:  Number of active public XML schemas
> 
> 
> I have often thought about the concept of dynamically generated WSDL
> documents, for cases in which more ad-hoc interaction among systems
> needs to occur, perhaps driven by the context of a request. 
> But I think
> we're a ways off from that in terms of standards and products 
> - if it is
> indeed a useful concept.


Another case of dynamic generation is translation between schema languages.


An example is the X.694 standard, which specifies a translation from XML
Schema to ASN.1.  There has been a proposal to standardize the reverse
translation as well.

However, in the case of X.694, the fact that the source syntax is XML does
not play a significant role.  X.694 converts abstract **schema components**
to equivalent ASN.1 constructs, so it doesn't really deal with the XML
representation of XSD.  (Before applying X.694, schema documents must be
converted to abstract Schemas as specified in the XML Schema
Recommendation.)

***

In general, I think that the use of XML for a new formal language designed
primarily for human consumption may or may not be a good choice.  There are
pros and cons to it.

Using XML can facilitate the creation/specification of a new language, the
development of early tools for the new language, and the learning of the new
language.  On the other hand, an adequate non-XML syntax can make the
language more usable by those who have learned it.

Recently, I developed a specification of an ad-hoc language for conformance
testing, and decided to use an XML syntax for it.  I felt this was very
appropriate in that case, because it makes the language simpler.  It took me
less time to write the specification, and it will take less time to whomever
will implement it.  The instances of use of the language (conformance
assertions) will be rather verbose, but since it is a niche language, the
total number of hours that people will spend using the language (reading and
writing) will be very low.

I think the arguments "pro" an XML syntax, in a formal language designed
primarily for **human consumption**, become weaker if the language is
expected to be widely used.

Alessandro Triglia


> 
> Kind Regards,
> Joseph Chiusano
> Booz Allen Hamilton
> Strategy and Technology Consultants to the World
>  
> 
> > -----Original Message-----
> > From: Burak Emir [mailto:Burak.Emir@e...] 
> > Sent: Wednesday, November 03, 2004 6:56 AM
> > To: Michael Kay
> > Cc: 'Chizzolini Stefano'; xml-dev@l...
> > Subject: Re:  dynamically generated XML Schema?! Re: 
> >  R:  Number of active public XML schemas
> > 
> > Michael Kay wrote:
> > 
> > >>Who needs to dynamically generate schemas? The whole point 
> > of schemas 
> > >>is to be a widespread, well understood description of instances.
> > >>    
> > >>
> > >
> > >There was someone with that need writing to the list a few 
> > days ago. It
> > >  
> > >
> > I am aware of that request for help, but I disagree. You were 
> > suggesting 
> > to her that multiple schemas might do the trick.
> > 
> > >seems entirely legitimate to me to apply different schemas 
> > to the same
> > >document at different stages of a workflow, or for senders 
> > of documents to
> > >apply stronger validation criteria than recipients of the 
> > same documents.
> > >
> > >  
> > >
> > Granted, but does that require a "dynamically generated" schema?
> > 
> > By dynamically generated, I understand this: A clever way of 
> > doing many 
> > matrix multiplications is to use dynamic programming (ordering the 
> > multiplications once you know all the matrices' dimensions).
> > 
> > A web application may dynamically generate a response for a request.
> > 
> > In the use case you seem to suggest, senders seem to refine 
> > schemas to 
> > achieve tighter checking. If one knows in advance that one 
> wants such 
> > refinement, one can write the schemas by hand. If not, then 
> finding a 
> > mechanical transformation for the old schema will not help much.
> > 
> > I guess, the problem for that use case is modularity.
> > 
> > Coming back to "dynamically generated", I think the very fact that 
> > somebody can write a mechanical transform to generate one 
> schema from 
> > another hints at enough anticipation of requirements that the 
> > original 
> > schema could have been written in an extensible way in the 
> > first place.
> > 
> > regards,
> > Burak Emir
> > 
> > http://lamp.epfl.ch/~buraq
> > 
> > -----------------------------------------------------------------
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> > 
> > 
> 
> 
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> 


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