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From: Peter Eisentraut on 26 May 2010 12:41
On ons, 2010-05-26 at 11:47 +0100, Mike Fowler wrote:
> > The XMLEXISTS function works with XQuery expressions and doesn't have
> > the call signature that your patch implements
>
> Looking at the manuals of Oracle, Derby and DB2 I see how the call
> signature differs. I also note that Oracle's implementation is XPath
> only, Derby's is partial XQuery and DB2 appears to be full XQuery.
>
> What do people prefer me to do? I see the options as:
>
> 1) Change the call signature to match the standard
> 2) Change the function name back to xpath_exists

It would be nice to make XMLEXISTS work as in the standard, seeing how
many others are providing the same interface.

> Should option one be the more popular there's further choices:
>
> 1) Integrate XQuery support to completely match the standard, however
> this will require the addition of a new library libxquery
> 2) Leave the XPath as is, inline with Oracle's implementation
> 3) Hybrid approach. Since XML is a comple time option, add XQuery as
> another. Conditional completion gives the full XQuery support when
> available or just the XPath when not

I think providing XPath is enough, at least for now.



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From: mike on 1 Jun 2010 12:06
Quoting Peter Eisentraut <peter_e(a)gmx.net>:

> It would be nice to make XMLEXISTS work as in the standard, seeing how
> many others are providing the same interface.
>
....
>
> I think providing XPath is enough, at least for now.
>

Hi Peter,

From piecing together sections 8.4 (<XML exists predicate>) and 6.18
(<XML query>), I believe the full call signature would be (apologies
if my bracketing isn't right):

XMLEXISTS
(
xquery_expression
[
PASSING {BY REF|BY VALUE}
{ (xml_expression [BY REF|BY VALUE])
| (xml_expression AS identifier)
}
[, ...]
]
)

Seeing as we're only intereseted in XPath for the moment and most of
the syntax above is only really relevant to XQuery, I would suggest
the following as accepatable until full XQuery support comes:

XMLEXISTS
(
xpath_expression
[
PASSING BY REF xml_expression [BY REF]
]
)

There is one drawback in this approach, namely xml namespace support.
I think borrowing the solution used in the xpath() (i.e. passing a
nsarray) is out of the question as it won't be future proofed against
full XQuery support. This is because the declaration of namespaces in
XQuery is actually part of the query itself. I also think it
inappropriate to attempt to parse the xpath_expression looking for
XQuery style namespace declartions. So I think we ignore declared
namespace support for the moment and just get the syntax correct ready
for XQuery support in the hopefully near future.

Do you agree with what I have proposed?

Regards,
--
Mike Fowler



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