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RE: Should instance element be optional?

From: Micah Dubinko <MDubinko@cardiff.com>
Date: Tue, 15 Jan 2002 13:04:41 -0800
Message-ID: <E840F0B7E6189547BDB91DA8BF2228AB28C13A@csmail.cardiff.com>
To: "'werner.donne@re.be'" <werner.donne@re.be>
Cc: "'www-forms@w3.org'" <www-forms@w3.org>
Hi Werner,

The December WD did a poor job explaining this. The next one should be
better. It goes something like this:

* Instance data (as in XSLT) always has a "root node" which is _not_ an
element node, but rather performs the same function as the Document node in
DOM (i.e. doesn't correspond to any particular part of a serialized
document)
* Top level elements are children of this root node.
* There is always "instance data", even when there is no element
<xforms:instance>
* During initialization, the XForms processor creates the instance data
--quite easy when <xforms:instance> is provided--merely a copy-children
operation, otherwise:
  - each binding expression is treated as a simple name (slashes cause an
error)
  - one element node with a matching name is created per form control

For this simple UI:

<xforms:input ref="a">...
<xforms:input ref="b">...
<xforms:input ref="c">...

You get:

    /
    |
 |--+--|
 a  b  c

A tree with a root node, and element node children "a", "b", and "c".
Entered form data would live in additional text nodes underneath the
elements. Attempting to serialize this to XML (with @@@ representing entered
data) would yield:

<a>@@@</a>
<b>@@@</b>
<c>@@@</c>

Which is why the binding expressions ref="a", ref="b", and ref="c" work. But
it's _not_ well-formed XML, which needs to be singly-rooted. To get around
this, at submit the XML serializer inserts a wrapper element as needed
called <instanceData>, in no namespace, so that the submitted data on the
wire would look like:

<instanceData>
  <a>@@@</a>
  <b>@@@</b>
  <c>@@@</c>
</instanceData>

Which looks much like the example at the bottom of 2.3 in the December
draft.

Whew. This XML stuff gives me a headache. ;-)
Thanks, and please continue to provide your excellent feedback.

.micah



-----Original Message-----
From: Werner Donné [mailto:werner.donne@re.be]
Sent: Tuesday, January 15, 2002 6:03 AM
To: www-forms@w3.org
Subject: Re: Should instance element be optional?


Indeed, but I wonder what the rules mentioned in that section will be.
Something will have
to be generated for the instance data, otherwise the form controls are bound
to nothing.

Regards,

Werner.
-- 
Werner Donné  --  Re BVBA
Engelbeekstraat 8
B-3300 Tienen
tel: (+32) 486 425803	e-mail: werner.donne@re.be
Received on Tuesday, 15 January 2002 16:07:04 GMT

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