- 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 UTC