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RE: [xml-dev] Quiz: what's the value space of the <Publisher> element?

This is an old problem in database systems - see discussion of intention and
extension by CJ Date in Intro Database Systems.

The value space of Publisher may in fact be constrained by the extension
(all the values) in a Publisher table.

-----Original Message-----
From: Frank Manola [mailto:fmanola@acm.org] 
Sent: Monday, June 22, 2009 9:09 AM
To: Costello, Roger L.
Cc: 'xml-dev@lists.xml.org'
Subject: Re: [xml-dev] Quiz: what's the value space of the <Publisher>


Your claim seems to be along the lines of "the sky is falling".  Just  
because the legal values can't be determined "in isolation" doesn't  
make instance-document-generator tools "impossible", or even  
"extraordinarily difficult".  It just means the tools may to look at  
more of the schema.  If what you say were true, it would be impossible  
to use "assert" to enforce constraints at all, since one (inefficient)  
way of implementing your instance-document-generator tool would be to  
implement a tool that generated instances using the element  
declarations in isolation, and then run the resulting instances  
through an "assert-constraint-checker" and throw out the bad ones.  If  
such a constraint-checker can't be built, "assert" hasn't been  
specified properly.


On Jun 22, 2009, at 11:47 AM, Costello, Roger L. wrote:

> What this means is that an element declaration cannot be understood  
> on its own, in isolation.
> To understand an element you must understand all possible ancestors  
> of the element.
> Want to create a tool that automatically generates sample instance  
> values for each element declared in the schema? That's relatively  
> straightforward in XML Schema 1.0 because you can understand each  
> element declaration in isolation. In XML Schema 1.1, as the above  
> example illustrates, an element's value cannot be determined in  
> isolation. So, instance-document-generator tools become impossible.  
> (If not impossible, it will certainly be extraordinarily difficult)
> Want to create a tool that does automated analysis of element  
> declarations? That's intractable.  (If not intractable, it will  
> certainly be extraordinarily difficult)
> Comments?
> /Roge


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