XML Processing Model WG

Meeting 92, 15 Nov 2007


See also: IRC log


Norm, Alessandro, Richard, Henry, Rui, Andrew, Murray, Alex
Paul, Mohamed (partial)


Accept this agenda?

-> http://www.w3.org/XML/XProc/2007/11/15-agenda


Accept minutes from the previous meeting?

-> http://lists.w3.org/Archives/Public/public-xml-processing-model-wg/2007Nov/0031.html


Next meeting: telcon 29 November 2007

Alessandro gives regrets for 29 Nov

(Note that we are not meeting on 22 Nov!)

XPath versions

-> http://lists.w3.org/Archives/Public/public-xml-processing-model-wg/2007Nov/0038.html

Norm summarizes the state of play

Henry: The traditional schema group compromise seems appropriate: call attention to it in the next draft of the spec and ask for implementor and user feedback.

-> http://lists.w3.org/Archives/Public/public-xml-processing-model-wg/2007Nov/0053.html

Alex: So we're going to allow for different answers in the two versions.

Norm: Yes, for now, with Henry's suggestion for priority feedback

Henry: The 99.99% case is when you're comparing strings in XPath 1, one of the strings will coerce to a number. In that case, you will get the same answer.

Murray: Why can't we settle on XPath 2.0

Henry/Richard: Because right now there are too many implementation communities where 1.0 is only available.

Murray: I think it'd be better to leave them behind than to possibly give different results.

Henry: The proposal as it stands includes the idea that we give authors guidance for interoperability.
... It's extremely unlikely that the kinds of xpaths that don't interoperate will really turn up in practice.
... I'd rather include the XPath 1.0 people in at the expense of that very small problem than exclude them to get rid of it.

Alex: Interoperability is more than just getting the same answer; there are also cases where the XPaths simply won't work on some implementations.

Norm: I think saying XPath 2.0 only would be a tactical error.

Murray: So can we say 1.0 only?

Norm: There are implementors that only plan to support 2.0.

Alex: I'm not sure that guiding authors to use some squishy middle ground is the right answer.
... I think it'd be better to explain the interoperability problems.

Some discussion of the right interoperability story.

Henry: I'd like to see the editor try to write up the point that we arrived at.

Norm: Uh, I did that.

Alex: Do we want to allow the xpath-version attribute on any element?

Norm: I was thinking of cut-and-paste
... But I'm perfectly happy to try putting it only on p:pipeline-library and p:pipeline

Some discussion of what the differences between 1.0 and 2.0 actually are

Richard: Should we just make it a static error to attempt to use XPath 2.0 with an XPath 1.0-only processor?

Henry: I'm happy with the silent attempt because it is amenable to conditional pipelines.

Murray: Back in the days when we were first talking about SGML on the web, one of the expressions that came up was "perverse obscurity".
... This discussion of 1.0/2.0 corners is perverse obscurity.
... We're setting up a situation where it is possible for pipelines to generate the wrong answer.

Henry: I think you're exhagerating the situation.

Norm: I think the number of cases where you're going to give the wrong answer is quite small.

Richard: Presumably users of XSLT 2.0 processors with XSLT 1.0 stylesheets are experiencing the same problems.

Norm: yes.

Henry: I've been doing this for years and I've never had a problem.

Norm: We could make XPath 1.0 compatibility mode a MUST for implementors

Richard: And we could say that XPath 1.0 implemntors MUST only run expressions that will give teh same result

Norm: Bah, I don't think I want to go there.

Henry: I sort of like this road; nobody loses, it's just that some people win more than others.
... I think the spec should say that if someone asks for XPath 2.0 evaluation, your XPath 1.0 implementation MUST only evaluate those XPaths which they know have the same value.

Richard: And if yours doesn't know any, it must reject them all.

Norm: So we're going basically the route I outlined, but saying that 2.0 processor must implement 1.0 mode and a 1.0 processor must not evaluate any expression that it cannot determine will give the same result in XPath 2.0.

Richard: Can we find out what the subset is?

Alex: Maybe. There's an appendix in XPath 2.0 spec.

Proposed: Go forward as above for the next draft.


XSLT versions

-> http://lists.w3.org/Archives/Public/public-xml-processing-model-wg/2007Nov/0016.html

Norm outlines his plan

Alex: I'm all for it.

Proposed: go this way for the next draft.


New public working draft

Norm: I think we need a new draft asap.

Richard: We also need the stuff about what types are in scope.

Norm: I'm happy to do the next draft with a fair number of "TBD" sections.

Proposed: editor will make a new public draft with the XPath/XSLT decisions and as many other decisions as possible to be published as soon as practical.


New step types (p:hash, p:uuid, p:www-form-url(en|de)code

Norm: Anyone object to putting those in the next draft?

Mohamed, do we have strong use cases for them

Norm: Yes, and they're optional anyway


Other last call comments (implicit inputs/outputs; default bindings)

-> http://lists.w3.org/Archives/Public/public-xml-processing-model-wg/2007Nov/0032.html

Norm summarizes the state of default bindings


Norm attempts to summarize the default input/output case.

See 2.3 in the 13 Nov editor's draft.


<scribe> ACTION: Norm to change all the examples [recorded in http://www.w3.org/2007/11/15-xproc-minutes.html#action01]

Any other business

Henry: It occurs to me that wrt the visible step types, it's not completely clear whether we have schema rules or xslt rules. If I import something that imports something else, do I get to use what's in the third thing or not.
... Richard and my prose supposes that the answer is yes. The current draft suggests that it's no.
... And the message about circular imports clearly suggests that it's no.

Richard: I believe that Henry's message is right, modulo that fix.

Henry: I'd like to particularly encourage Alex to review it.

Alex: Right. Will do.


Summary of Action Items

[NEW] ACTION: Norm to change all the examples [recorded in http://www.w3.org/2007/11/15-xproc-minutes.html#action01]
[End of minutes]

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$Date: 2007/12/12 19:00:35 $