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The first question is whether an XML schema should be used to enforce
these constraints. Once you decide that then the next step is to use
schematron. Once you hit the limitations of that you're in 'writing
custom code at the various end points' land. Most developers skip the
Schematron step.
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PITHY WORDS OF WISDOM
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This posting is provided "AS IS" with no warranties, and confers no
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> -----Original Message-----
> From: Cox, Bruce [mailto:Bruce.Cox@USPTO.GOV]
> Sent: Monday, August 16, 2004 2:41 PM
> To: Bullard, Claude L (Len); Roger L. Costello; xml-dev@lists.xml.org
> Subject: RE: [xml-dev] Are people really using Identity
> constraints specified in XML schema?
>
> I, for one, am very interested in discussing these issues further.
> Since XML Schema data typing cannot express all the business
> rules that constrain, for example, patent document numbers
> (from about 100 issuing offices), what other technologies can
> be invoked that would? What combination of technologies
> should be used, and in what order, to accomplish the goal?
> I'm interested in standards-based technologies, such as XML
> Schema, to express such rules in a fashion that removes as
> much variation as possible among systems that implement them
> around the world. Should we use a repository for the rules
> and their implementations?
>
> Is anyone else interested?
>
> Bruce B. Cox
> U.S. Patent & Trademark Office
> SA4XMLT
> +1-703-306-2606
>
> -----Original Message-----
> From: Bullard, Claude L (Len) [mailto:len.bullard@intergraph.com]
> Sent: Friday, August 13, 2004 12:35 PM
> To: 'Roger L. Costello'; xml-dev@lists.xml.org
> Subject: RE: [xml-dev] Are people really using Identity
> constraints specified in XML schema?
>
> Michael is right, but this isn't a one size fits all decision.
> Loose filters allow dirt to seep into the system. The
> architectural question is what are the right places to put
> such rules into a system?
> We are aware of different technologies for this, and it is a
> good thread to out the issues if that interests the members
> of this list.
>
> That a technology can accomplish a task doesn't mean it is
> the right tech for that task. It doesn't mean it isn't.
> I suspect this is another task situatedness issue, but given
> a services architecture, one might want to inquire about
> tasks relative to their roles in distributed processes that
> are candidates for orchestration.
>
> len
>
>
> From: Roger L. Costello [mailto:costello@mitre.org]
>
> Michael Kay wrote:
>
> > I tend to be a little wary of constraints myself.
> > Many of those you see in student textbooks are misguided.
> If I see a
> > schema (XML or RDB) with the constraint that employees must be over
> > 16, I ask myself what the IT department would do if the business
> > decided to hire someone under 16. If there's a rule that an
> employee's
> > manager must themselves be an employee, I ask what would
> happen when
> > someone is told that they now report to a contractor.
>
> This is excellent:
>
> > It's not the job of computers to limit what people are
> allowed to do
> > (or the job of the IT department to regulate the business).
>
> The following innocuous sentence has profound implications on
> the role of schemas:
>
> > A guideline I use is that constraints should be there only
> to protect
> > the IT system itself from data that it cannot handle.
>
> Would you elaborate upon this sentence Michael? I believe
> that you are saying that the role of a schema is to define
> things such as:
> - ensure that a "date" is indeed a valid date
> - ensure that an "age" is indeed a valid age
>
> The role of a schema is not, for example, to specify:
> - the "age" must be at least 16.
>
> So, your guideline says: use schemas to specify datatypes for
> objects, not their range of values. Is that a fair summary
> of your guideline? /Roger
>
>
>
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