W3C Forms teleconference December 19, 2007

* Present

Charlie Wiecha, IBM
Erik Bruchez, Orbeon
John Boyer, IBM (chair)
Leigh Klotz, Xerox (minutes)
Mark Birbeck, x-port.net
Nick van den Bleeken, Inventive Designers
Uli Lissé, Dreamlabs
Keith Wells, IBM
Blake Jones, DAISY/ViewPlus
Sebastian Schnitzenbaumer, Dreamlabs

* Agenda


* Previous Minutes

* Next Teleconference

John Boyer: Our next telecon is January 9, 2008. It starts 15 minutes earlier and runs 15 minutes later in your time zone.

* Offlist ping about answer for charset and encoding (action MarkB on May 2)


Mark Birbeck: I'll try to get to this before we break for the year.

* Proposal for XForms 1.2 to allow custom function definitions

(and don't add functions like decimal-string() and sum-product()) http://lists.w3.org/Archives/Public/public-forms/2007Dec/0035.html http://lists.w3.org/Archives/Public/public-forms/2007Dec/0038.html

John Boyer: Thanks to Erik, Uli, and Nick for holding the email discussion. Nick pointed out that we might need to define custom functions.
Erik Bruchez: Both XQuery and XSLT 2.0 support it; even custom functions in XSLT. The idea is that you use the constructs to define a function you can use any place you have XPath expressions (style sheet, model). We might be less tempted to add functions all over the place; you can achieve re-use by writing your own function. XSLT and XQuery are quite complete languages and XForms is not, so I'm not sure of the details. The simplest thing would be a way to assign a function as another XPath expression.

John Boyer: I like the extension idea. Or a way of wrapping XForms actions, and not have them mutate objects other than in the functions. Then you can use @if and @while.
Erik Bruchez: I think that would be good to be able to use actions. Not being able to re-use sequences of actions with parameters is a problem; you can re-use actions by dispatching to the model, but without parameters or return values. You have to use hack instances and it's awkward.
John Boyer: The xforms:function concept could easily use xforms:param or something els like XSLT templates. We'll get pushback if we don't make a limitation that the function can't have side effects. So we could limit it to the instance inside the function.
Erik Bruchez: In XPath you want them side-effect free as well. But imagine a function that returns void (empty sequence, empty nodeset) which does actions. If there were a way, it would cover some use cases, but I'm not sure how. But extension functions can have side effects. At the low level of the implementation, XPath allows side effects.
John Boyer: So there is a way to signify that there are side effects? That runs roughshod over our ability to track dependencies.
Erik Bruchez: I don't know if it's in the spec.
John Boyer: We got into trouble with Michael Kay over XPath before with the random and now functions. Modifying the instance is even more egregious.
Erik Bruchez: With XQuery and XSLT 2.0 it's all XPath 2.0; Michael Kay says they don't really differentiate between XSLT 2.0 elements and XPath functions. ... and the value is an XPath expression. So you could get pushback.
John Boyer: It reminds me that we need to tell the difference between side effects or not. That reminds of of Pascal procedures vs. functions. We could have functions being side-effect free and procedures a reusable set of actions, and get around the parameter problem. Anybody else have opinions?
Leigh Klotz: I think we should focus on the interface and not the implementation and consider this part of the interface to XForms, and then towards being able to add libraries of custom libraries.
John Boyer: I think that is a separate feature; if you want to be able to write something that works everywhere, we have a way to do that.
Leigh Klotz: I think they're two separate problems and we should try to think of them separately and make sure it meets in the middle. There are three things: how and what we add (and we have identified two nascent points: XPath functions and actions), how they are specified (the inflection point) and then how to implement them, and on that last one, wholly self-contained implementations may be possible for many, but we should also allow native or external implementations (JavaScript or internal) which will encourage the development of function libraries as it has for XSLT.
John Boyer: Nick, anything to add.
Nick van: [irc] I'm agreeing with it
John Boyer: Should we do this for XForms 1.2?
Nick van: [irc] but what we do then with sumproduct?
Mark Birbeck: I'm agreeing too. The sooner we start addressing reusability the better.
John Boyer: It's not easing on-the-glass but it does ease authoring.
Nick van: It's my feeling too. If we don't add it in 1.2 then we still have the problem with sumproduct in 1.2. That's the main reason I proposed the ability to define functions.
John Boyer: It shoots the necessity of adding sumproduct, decimalstring, and others we haven't come across. It addresses reusability and Erik's way of having an easier way to invoke things.
Nick van: We can add a list of them in an appendix just like XSLT has.
John Boyer: Yes, as Leigh says, a native implementation can be faster and an implementation could decide to use it.
Leigh Klotz: I'm hearing namespaces there. It's just like in XSLT and exforms.org.
John Boyer: I think we have a proposed resolution to work on this for XForms 1.2.
John Boyer: Proposed Resolution: Add to XForms 1.2 the capability to express function and procedure interfaces and implementations.

Leigh Klotz: Are actions and xpath the only two points we plug things in?
John Boyer: Those are the only two things with regard to side effects; either have them or they aren't.
Leigh Klotz: Are xpath expressions (model and ui) and actions the only two places? What about presentation controls as in XBL? Or are we far enough away from presentation by being abstract.
John Boyer: So the eventing paradigm might be one, the event handlers.
Leigh Klotz: That's events again. I just want to make sure there's enough places.
Mark Birbeck: In XML Events 2 we added the ability to add have script inside action sequences. So, it means that the distinction among action, script, and function starts to blur. And secondly, I wonder if we can make use of it to allow calling an action from an XPath expression.
Leigh Klotz: There's also validation; Schematron plugs XPath into other Schema languages. We use XPath for that already, but can we plug in new functions there? Or how about serialization? I want to make sure that it's not just xf:action/* and */[@nodeset or @ref or @value] that we can use.
John Boyer: Can we get some wording?
Leigh Klotz: "Add to XForms 1.2 the capability to define interfaces to and implementations of extensions for both side-effect and side-effect-free operations, along with the specification of which points these extensions may be invoked, including but not limited to XPath expressions and actions."
John Boyer: Good. [irc] CharlieWiecha, John_Boyer, ebruchez, Nick, wellsk, Blake, markbirbeck, Schnitz.
John Boyer: So resolved.

Resolution 2007-12-19.1: Add to XForms 1.2 the capability to define interfaces to and implementations of extensions for both side-effect and side-effect-free operations, along with the specification of which points these extensions may be invoked, including but not limited to XPath expressions and actions.

John Boyer: Who wants to take the action item to pull together some spec-ready text?
Erik Bruchez: We should come up with a proposal for syntax first.
John Boyer: I agree. It'll take a couple of iterations. You could write sumproduct or decimal string as examples.
Erik Bruchez: I am not sure I can commit to write the whole thing but I can get the ball rolling for how to declare a procedure in the XForms model.
Nick van: [irc] sounds perfect for me
John Boyer: Nick you want to do it?
Nick van: No, Erik will do.
Leigh Klotz: I will go look for more places to add it.
John Boyer: Sounds like two actions.
John Boyer: Erik, can you own this?

Action 2007-12-19.1: Erik Bruchez to send email to write up initial draft for extensions.

Action 2007-12-19.2: Erik Bruchez to produce spec-ready text for XForms 1.2 extensions.

Action 2007-12-19.3: Leigh Klotz to investigate and report on possible uses for extension functions outside of xf:action/* and */[@nodeset or @ref or @value].

* Proposal to let XPath 2.0 be used with XForms 1.2 via a modularization approach


Erik Bruchez: If we delay XPath 2.0 to XForms 2.0, then it may take years. If we add function libraries it may be less important. However, we still need it. In the XProc work we are doing with W3C, based on feedback from Michael Kay and others, we decided to allow either 1.0 or 2.0 and specify in the program whether the form author is requesting 1.0 or 2.0. There is decision logic in the spec that gives maximum flexibility to authors and implementors. I think we can do this before XForms 2.0. Also, if we have a big spec, then it will take a long time to get there. Our experience with XPath 2.0 shows you can integrate it in a light-weight way with most of the benefits. So I think it would be a good idea to try to specify XPath 2.0 support in modular way on top of XForms 1.1 or 1.2.
Nick van: [irc] we maybe even want to allow different languages for the query (to specify node sets and refer nodes), constraint and calculation language
John Boyer: In the XML Signatures recommendation they had different algorithms at different requirement levels. For filtering, for example, there were "should" and "may" and "must". So we may want to talk about an optional XPath 2.0 binding.
Nick van: [irc] If we do add XPath 2.0 I would prefer we first try if we could add support for pluggable languages
Erik Bruchez: It may give implementors more confidence to move in this direction if we have something earlier; otherwise, they will wait 5 years before looking at it.
John Boyer: The scarey bit for me is XPath 2.0 in an XPath 1.0 processor even though it specifies a 1.2 processor. So maybe there is a versioning capability and it requires some pluggable module as Nicks says, not just functions, but other equipment such as XPath 2.0.
Erik Bruchez: XPath is a fundamental part of XForms so an attribute for that is fine for me. If you say XPath 2.0 is mandatory for XForms 2.0, and you don't have XForms 2.0 then it won't work anyway.
John Boyer: Absolutely, but it could be more generic: xpath-2.0, javascript, etc.
Mark Birbeck: [irc] But could also support JSON, for example. Perhaps my @hasFeature proposal from years ago?
Erik Bruchez: Can we quickly do this as a separate document under our charter?
John Boyer: We can double check with Steven, but my prior experience is that we can produce other documents in support of the charter requirements.
Nick van: Or a note.
John Boyer: It would be nice to have the content first. The XML Signature WG produced a plethora of products: XML Canonicalization, Exclusive Canonicalization, and XPath Filter 2, which bears some relationship to our issue, of using another technology with our existing recommendation track.
Leigh Klotz: I like XPath 2.0 and Erik's proposal sounds like a good way to get people to look at it early.
John Boyer: No resolution, but an action to look at the module. I'm not sure we can backport it to 1.1 because of the Schema change for @hasFeature or whatever. Erik:

Action 2007-12-19.4: Erik Bruchez to investigate adding XPath 2.0 to XForms 1.2 in a modular way that encompasses adding other pluggable languages in the future.

John Boyer: OK, see you all in the new year.

* IRC Minutes


* Meeting Ends