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   XML Schemas : Constraint mecanism on complexType ?

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  • From: Bruno Chatel <bcha@chadocs.com>
  • To: xml-dev@lists.xml.org
  • Date: Thu, 23 Nov 2000 12:44:28 +0100


The confrontation of my experience with DTD and the new features
available with XML Schemas shows me that a very interesting step
is to be done. This point of view concerns particulary the possibility
to specify in the data model contrainsts on content (simple types and
facets mecanism) [but i appreciate the type modeling mecanism too ;-)].

Usually in XML applications (and previously in SGML applications),
we need to control the document more precisely than according to
a possible structure : this functionality must then be developed in
a specific module (dependant of the application, and then implying
many different mecanisms and development languages because
integrated in a larger project). With XML Schemas, the way to specify
contrainsts is now in a model (independant of the general project 
environment). Very interesting.... But, incompleted.
Indeed, with the current specifications, we are not able to define
contrainsts on structures (except usual constraints on element order,
element occurs, ect...). In fact, I need a mecanism allowing me to
declare something like "If the left sibling (with GI T1) of the parent node
of the curent node has an attribute named CONTEXT and attribute value 
is ACTIVE, then the first child of the current node must have a empty
The only way to do this today is to code it in an applicative (project dependant)
program (or module).  It would be very good if we may write this
outside of a specific (and personnal) module.
Do you think that this functionnality is too complex for a modeling mecanism ?
May I expect such kind of functionality in future Schema evolutions ?
Thanks for your ideas about this.

-- bruno--
Bruno Chatel
Tel : (+33)[0] 4 96 11 14 57
Email : bcha@chadocs.com


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