RE: [xml-dev] Are people really using Identity constraints specified in XML schema?

["Cox, Bruce" <Bruce.Cox@USPTO.GOV>]

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