W3C home > Mailing lists > Public > public-xml-processing-model-wg@w3.org > October 2009

XProc Minutes 22 Oct 2009

From: Norman Walsh <ndw@nwalsh.com>
Date: Thu, 22 Oct 2009 12:08:38 -0400
To: public-xml-processing-model-wg@w3.org
Message-ID: <m23a5bwgvt.fsf@nwalsh.com>
See http://www.w3.org/XML/XProc/2009/10/22-minutes

[1]W3C

                                   - DRAFT -

                            XML Processing Model WG

Meeting 157, 22 Oct 2009

   [2]Agenda

   See also: [3]IRC log

Attendees

   Present
           Norm, Mohamed, Henry, Paul, Vojtech

   Regrets

   Chair
           Norm

   Scribe
           Norm

Contents

     * [4]Topics

         1. [5]Accept this agenda?
         2. [6]Accept minutes from the previous meeting?
         3. [7]Next meeting: telcon 29 Oct 2009
         4. [8]Telcon facilities at TPAC
         5. [9]XProc versioning proposals
         6. [10]Any other business?

     * [11]Summary of Action Items

   --------------------------------------------------------------------------

  Accept this agenda?

   -> [12]http://www.w3.org/XML/XProc/2009/10/22-agenda

   Accepted.

  Accept minutes from the previous meeting?

   -> [13]http://www.w3.org/XML/XProc/2009/10/15-minutes

   Accepted.

  Next meeting: telcon 29 Oct 2009

   Paul gives regrets.

   Norm: Telcon of 5 November is cancelled.

  Telcon facilities at TPAC

   Norm: Confirmed.

  XProc versioning proposals

   ->
   [14]http://lists.w3.org/Archives/Public/public-xml-processing-model-comments/2009Oct/0074.html

   Norm summarizes

   Norm: Three clearly open questions: where is @version allowed, does
   use-when count inside a p:inline, do we do any static analysis on
   p:when/p:try blocks when they contain invalid steps.
   ... Any other questions or comments?

   Vojtech: What about the importing of the standard step library.

   Norm: I think we should not allow importing of declarations for the
   builtin steps.

   Henry: I think that's right.
   ... On a larger scale, I'm uncomfortable with the upward percolating
   invalid story.
   ... I worry that it isn't complete or correct. I would like to identify
   that aspect of this proposal as a feature at risk.
   ... so that we can jettison it without going back to last call again again
   if we remove it.

   Norm: I'm perfectly happy to do that, but I can't think of any static
   meaning for a subpipeline with an invalid step that will absolutely be
   executed.

   Henry: Right. I think use-when is the only thing that will work and I want
   to be able to jettison all the invalid stuff without going back to last
   call.

   Vojtech: I agree with Henry, I think the results are going to be
   unpredictable.

   Norm: Ok. I'm happy with that. Or we could just pull it all out now.

   Vojtech: There's still this story about the unknown ports. You have steps
   that you recognize but they have unknown ports.
   ... We could say you have to use use-when there, or we could keep the new
   story about defaults.

   Henry: The motivation for doing our best here came from Jeni.

   Norm: Jeni is happy with the proposal:
   [15]http://twitter.com/JeniT/status/4898625357

   More discussion.

   Norm mumbles about some folks wanting to be able to use pipelines without
   changing them.

   Norm uses the "messages" output port on p:xslt as an example.

   Henry: That use case is interesting because it doesn't need a p:choose.
   You don't get the messages, but maybe you're willing to live with that.
   ... I can just about see that. But I think as far as the steps I've never
   heard of story, that's never going to work.
   ... There's never going to be a graceful fallback.
   ... If we're not going to do the whole thing, I think the new ports case
   is worth keeping, but lose all the "upward percolation" of invalid p:*
   steps.

   Vojtech: If the processor sees an unknown step from the p: namespace, I
   think you just can't know what it means. I would force the pipeline author
   to use use-when in that case.
   ... But if the pipeline contains only known steps with new ports, then I
   think the simple defaulting story can be made to work there.
   ... It's not hard to implement and it's predictable.

   Norm: Does anyone want to argue for the more complicated story on this
   call right now.

   Henry: I think the fact that you can't tell if the first child of a
   p:declare-step is a new step or some sort of new name for p:variable makes
   it very hard to decide what to do.

   Vojtech: There may be unknown elements that effect the dependency graph.

   Norm: Ok. I'm willing to concede that use-when and the more complicated
   invalidation store are two ways to do the same thing.
   ... so maybe we should just do the simpler thing. You *have* to change the
   pipeline in some way, so you might as well change it in the way that's
   completely predictable.
   ... So the proposal on the table now is the one I made, modified to remove
   the "upwards percolating" invalid story for unknown step types.

   Vojtech: For unknown XProc elements.

   Norm: Is anyone unhappy with that change?

   Mohamed: I think I still have to go through. My former proposal was to try
   to get rid of use-when. My understanding is that use-when is pretty hard
   for users to understand.
   ... So I think I just cannot agree without knowing what we're going to say
   about use-when.

   Henry: In almost any case, the outcome of this discussion is going to be a
   new draft.

   Mohamed: My idea is that the use-when should not be used everywhere. It
   should have another name. And it should only be used on when or try/catch.
   ... A use-when is way more poweful than the problem we have to solve.

   Norm: We could do that, but I'm not sure it's necessary.

   Mohamed: I think we should just say that if the attribute
   "must-understand" is provided on p:when, then this branch shouldn't be
   analyzed in V.x. It's use-when but it's less powerful and solves just the
   use case we have.

   Vojtech: One problem with this story is, suppose in V2 we introduce a new
   element for an option or something and that one you can't put in a
   p:choose. You can do that only with steps.

   Henry: If we go back to the original observation that we're trying to
   handle the unexpected, a simple, general mechanism is probably the best
   approach.
   ... The other thing is, there's a lot to be said for leveraging experts
   understanding of difficult material and use-when is already there.

   Norm: I think that's a good point.

   Vojtech: What I like about the use-when proposal is that it's something
   that will be valid in new versions.
   ... We could ask on xproc-dev

   Mohamed: I want to have an explicit mechanism, but I think use-when is a
   real nightmare for tools that help users build their pipeline.

   Henry: I don't have much experience with use-when in XSLT, but the
   semantics seem quite clear to me.
   ... It's the opposite of XInclude, "this tree isn't here."
   ... I can see where some some complexity might arise in XSLT with
   templates and literal constructors, but we don't have that problem.

   Mohamed: My problem is that we can make pipelines that will have
   completely different connections depending on the version of XProc that
   you're using: consider putting use-when on a p:pipe inside a p:source.

   Norm: I think Mohamed's point is that you can nest two effectively
   completely different pipelines in the same file.

   Vojtech: It's true that use-when is a tool for forwards-compatibility, but
   it's also a much more general tool: you can use it to make pipelines that
   are compatible across different implementatins. I don't know if that's
   good or bad.

   Norm: I appreciate that Mohamed has reservations, but I don't hear
   consensus moving away from use-when on this call.
   ... I'd like to say that the consensus of the wG seems to be that they
   want to see a draft with use-when, so let's try to move forward that way.
   ... So let's close the open questions. Where is a version attribute
   allowed?
   ... Proposal: On p:pipeline, p:library, and p:declare-step. No where else.
   And required on the document element of a pipeline document.
   ... I can live with that.

   Accepted.

   Norm: Second question: what are the semantics of use-when inside a
   p:inline?
   ... Proposal: it's treated just like any other attribute and has no
   special semantics.

   Vojtech: So take the http-request step, suppose we add something to the
   c:request element.

   Norm: You wouldn't be able to do that all in p:inline, you'd have to build
   it up in some explicit way.

   Accepted.

   Norm: We're throwing out the whole backwards-chaining invalidation story,
   so the last question no longer applies.

   Vojtech: We already decided that importing the standard library is not
   allowed.

   Norm: Yes
   ... Anyone object to that?

   None heard.

   <scribe> ACTION: Editor to write this up as a new draft. [recorded in
   [16]http://www.w3.org/2009/10/22-xproc-minutes.html#action01]

  Any other business?

   None heard.

   Adjourned.

Summary of Action Items

   [NEW] ACTION: Editor to write this up as a new draft. [recorded in
   [17]http://www.w3.org/2009/10/22-xproc-minutes.html#action01]

   [End of minutes]

   --------------------------------------------------------------------------

    Minutes formatted by David Booth's [18]scribe.perl version 1.135 ([19]CVS
    log)
    $Date: 2009/10/22 16:07:07 $

References

   1. http://www.w3.org/
   2. http://www.w3.org/XML/XProc/2009/10/15-agenda
   3. http://www.w3.org/2009/10/22-xproc-irc
   4. http://www.w3.org/XML/XProc/2009/10/22-minutes#agenda
   5. http://www.w3.org/XML/XProc/2009/10/22-minutes#item01
   6. http://www.w3.org/XML/XProc/2009/10/22-minutes#item02
   7. http://www.w3.org/XML/XProc/2009/10/22-minutes#item03
   8. http://www.w3.org/XML/XProc/2009/10/22-minutes#item04
   9. http://www.w3.org/XML/XProc/2009/10/22-minutes#item05
  10. http://www.w3.org/XML/XProc/2009/10/22-minutes#item06
  11. http://www.w3.org/XML/XProc/2009/10/22-minutes#ActionSummary
  12. http://www.w3.org/XML/XProc/2009/10/22-agenda
  13. http://www.w3.org/XML/XProc/2009/10/15-minutes
  14. http://lists.w3.org/Archives/Public/public-xml-processing-model-comments/2009Oct/0074.html
  15. http://twitter.com/JeniT/status/4898625357
  16. http://www.w3.org/2009/10/22-xproc-minutes.html#action01
  17. http://www.w3.org/2009/10/22-xproc-minutes.html#action01
  18. http://dev.w3.org/cvsweb/~checkout~/2002/scribe/scribedoc.htm
  19. http://dev.w3.org/cvsweb/2002/scribe/

Received on Thursday, 22 October 2009 16:09:24 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Thursday, 22 October 2009 16:09:25 GMT