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Need for a 'global instance' function [was Re: i18n, componentized forms and multiple models]

From: Mark Birbeck <mark.birbeck@x-port.net>
Date: Mon, 24 Jul 2006 22:27:41 +0100
Message-ID: <640dd5060607241427y3149ef68hbb2397f897fe90d8@mail.gmail.com>
To: www-forms@w3.org


Just so that we don't lose one of Andrew's key points though, he does
rightly flag up that there is no way in XForms to get values from one
model into calculations in another model, or to use another model to
provide template nodes for copying via xf:insert, and so on. There is
no reason not to allow this, and in fact there are many, many
situations where we positively need it.

I would say that the main justification *for* is that once you get to
forms of a certain complexity they are just far too difficult to build
and maintain by hand. At this point you need to generate them, and to
do that you will invariably want to use models to provide
encapsulation. As it happens, even if your forms aren't that complex,
if you want to reuse features across many forms, it makes sense to use
multiple models.

For a fuller description of using models to provide encapsulation and
reuse, see my previous post at the end of the following thread, on
"Use cases for multiple models":


By the way, I'm not saying that we should allow cross-model
dependencies... well, I'm not saying that today, at least ;). In
formsPlayer we provide a globalInstance() function that allows you to
make a reference to an instance that is in any model, but as with
calling the now() function, it's not dynamic, and so the author needs
to be aware that they may need to use rebuild in certain situations.
But in simple situations like the one we have here, where you just
want to use a model to hold the user's preferences which are in turn
used for submissions, then rebuild is simply not a problem, and
globalInstance can be used straightforwardly.



On 24/07/06, Erik Bruchez <ebruchez@orbeon.com> wrote:
> Andrew,
>  > I'm testing the form on both Orbeon's Presentation Server (current
>  > release) along with Mozilla XForms 0.5 (0.6 said it had an invalid
>  > checksum and wouldn't install for me) in case it matters.  I don't
>  > really think it does, because one of the points in Dubinko's book
>  > was "options for cross-model communication are limited."
>  > Unfortunately, I can't find much on what those options are.  I
>  > suppose I could resort to using some JavaScript to solve the
>  > problem, but I would really rather not do it that way.
> If you download the latest OPS nightly build [1], go to the DMV Forms
> example, and open a form, you will see there what I think is a really
> cool illustration of i18n with a dropdown allowing you to switch at
> runtime between English and French resources (he he, this is not
> something you see often, to say the least, and XForms makes it a
> breeze to achieve).
> As suggested by others, simply load your initial resources into an
> instance (alternatively, you can run a submission upon xforms-ready):
>    <xforms:instance id="resources-instance" src="resources_en.xml"/>
> There is another instance holding the current language:
>    <xforms:instance id="language-instance">
>        <language xmlns="">en</language>
>    </xforms:instance>
> There is an xforms:select1 to change the language:
>    <xforms:select1 ref="instance('language-instance')">
>        <xforms:label
> ref="instance('resources-instance')/labels/language-choice"/>
>        <xforms:item>
>            <xforms:label>en</xforms:label>
>            <xforms:value>en</xforms:value>
>        </xforms:item>
>        <xforms:item>
>            <xforms:label>fr</xforms:label>
>            <xforms:value>fr</xforms:value>
>        </xforms:item>
>        <xforms:send ev:event="xforms-value-changed"
> submission="update-language-submission"/>
>    </xforms:select1>
> which runs a submision that updates the resources:
>    <xforms:submission id="update-language-submission"
> ref="instance('language-instance')"
>            action="/forms/service/resources/{.}" validate="false"
>            method="get" replace="instance" instance="resources-instance"/>
> All the internationalized resources in the page are referred to with
> things like:
>    <xforms:output ref="instance('control-instance')/message"/>
>    <xforms:label
> ref="instance('resources-instance')/labels/language-choice"/>
> This is much more flexible than to hardcode xml:lang in the page, and
> it works like a charm.
> I hope this helps,
> -Erik
> [1] http://forge.objectweb.org/nightlybuilds/ops/ops/
> --
> Orbeon - XForms Everywhere:
> http://www.orbeon.com/blog/

Mark Birbeck
x-port.net Ltd.

e: Mark.Birbeck@x-port.net
t: +44 (0) 20 7689 9232
w: http://www.formsPlayer.com/
b: http://internet-apps.blogspot.com/

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Received on Monday, 24 July 2006 21:27:50 UTC

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