RE: XPath conformance? was RE: [xml-dev] storing XML files

[Chris Parkerson <chrisp@exceloncorp.com>]

Agreeing with Evan, the way to extend XPath is to use XPath extensions
as defined by the W3C.  The way to extend XSLT is to use XSLT
Extensions.  It's very nice to have that capability (something missing
from many other standards that can be argued made their acceptance
limited).  I've seen use of these extension capabilities done in many
useful ways, both in XYZFind's product as well as other products.  Being
"creative" with and "extending" the CORE syntax of a language has caused
problems in the SQL world, caused the object database world to never
agree on standards (OQL... YIPE!), as well as fights in other realms.
Microsoft couldn't beat Java, couldn't claim ownership to C++, so now we
have C#... go figure ;->

As far as taking it to xmldb@xmldb.org, that would be fine, but that
would also imply that the issues here are completely separable from
issues facing XML technologies in general.  I do not believe that is the
case given the infancy of everything XML.  We are intertwined, and
issues such as this do not affect just the niche of the XML database
market.

Cheers,
Chris

---------------------------------------
Chris Parkerson
Product Manager
eXcelon Corporation
Burlington, MA
(781) 674-5393
http://www.exceloncorp.com
---------------------------------------


-----Original Message-----
From: Evan Lenz [mailto:elenz@xyzfind.com] 
Sent: Tuesday, October 09, 2001 1:08 PM
To: Champion, Mike; xml-dev@lists.xml.org
Subject: RE: XPath conformance? was RE: [xml-dev] storing XML files

Mike Champion wrote:
> I'd submit that a processor that executes legal XPath expressions "is"
an
> XPath processor, whatever it's called, and whatever superset of
> XPath syntax
> it also supports.

Because XPath can be extended via an extended function library, a la
XSLT
and XPointer, I would disagree with the claim that a processor that
supports
an extended *syntax* is in compliance with the XPath specification.

There are parts of the picture that are not standardized--most notably
how a
node-set (or even a boolean, for that matter) should be serialized.
These
are implementation-dependent (whether the implementation is the XSLT
specification or some XML database vendor).

This leaves vendors much freedom (at the expense of having a standard).
However, they should not feel free to extending the syntax of XPath,
i.e.
what the XPath spec *does* standardize.

For example, the following is not in compliance with the XPath spec:

/customer[name ~= "Mike"]

whereas this alternative expression would be perfectly fine:

/customer[ext:like(name, "Mike")]

Evan Lenz
XYZFind Corp.


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