Fw: Section 7 (PR#139)

Hi Erik,

Here is a response from Michael Kay that is quite informative regarding 
the kinds of things you would need to keep in mind while formulating a fix 
for issue #139.

He's clearly right about missing namespace prefixes of course (I basically 
forgot to list that, so do double-check the actual XPath 1.0 context 
definition).

Also, if I read correctly, he is pointing out that type mismatches can 
occur, and could be viewed as static or dynamic.  The two examples of type 
mismatches that he gave are parameters (e.g. count receiving a string) and 
invalid caste operations (e.g. union of non-nodeset).

If the wording is done well, I think we may not have to make the 
distinction, i.e. we do not have to care whether a particular XPath 1.0 
implementation treats these as static or dynamic. 

I think the more careful wording should take the form of saying that at 
all times the exception occurs *when the XPath evaluation is performed*. 

Cheers,
John M. Boyer, Ph.D.
STSM: Lotus Forms Architect and Researcher
Chair, W3C Forms Working Group
Workplace, Portal and Collaboration Software
IBM Victoria Software Lab
E-Mail: boyerj@ca.ibm.com 

Blog: http://www.ibm.com/developerworks/blogs/page/JohnBoyer


----- Forwarded by John Boyer/CanWest/IBM on 10/24/2007 12:33 PM -----

"Michael Kay" <mike@saxonica.com> 
Sent by: www-forms-editor-request@w3.org
10/24/2007 12:29 PM

To
"'John Boyer'" <xforms-issues@mn.aptest.com>
cc
<w3c-xml-query-wg@w3.org>, <www-forms-editor@w3.org>
Subject
RE: Section 7 (PR#139)







That's fine.

Undefined namespace prefixes are another possibility, in case you are
enumerating them. 

In fact XPath 1.0 doesn't distinguish very carefully between static and
dynamic errors, so count("xyz") is an error that can be reported either
statically or dynamically, similarly ($x|3).

Michael Kay

> -----Original Message-----
> From: John Boyer [mailto:xforms-issues@mn.aptest.com] 
> Sent: 24 October 2007 20:00
> To: mike@saxonica.com
> Cc: w3c-xml-query-wg@w3.org; www-forms-editor@w3.org
> Subject: Re: Section 7 (PR#139)
> 
> Hi Michael,
> 
> The working group agrees that this is a problem and will fix 
> it in the specification.  For XPath 1.0, the static errors 
> appear to be limited to expression well-formedness, undefined 
> variable references and undefined function references as 
> issues with the [context node, position, size] are handled 
> separately, i.e. their non-availability implies not executing 
> the xpath and behaving as if empty nodeset were returned.
> 
> Please let us know if you have any further concerns about this issue.
> 
> Thank you,
> John Boyer
> 
> > 
> > 
> > 
> >     D. "XPath expressions that are not syntactically valid": should
> >     cover all static errors, not just syntax errors. (Other static
> >     errors include, for example, references to functions or 
> variables
> >     not present in the context, and type errors detected 
> statically).
> > 
> > 
> > 
> >