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Re: XForms:instance requests, the HTTP Accept header and RESTful Web Services...

From: Lars Oppermann <Lars.Oppermann@Sun.COM>
Date: Fri, 19 Oct 2007 14:33:51 +0200
To: Philip Fennell <Philip.Fennell@bbc.co.uk>, www-forms@w3.org
Message-id: <4718A42F.5020900@sun.com>

Hi Philip,

We talked about your issue during the last WG call...

Generally, what you are looking for is supported in xforms 1.1 submissions by 
using the header element, through which the accept header can be set as needed 
by your content negotiation. There is currently no capability of specifying 
accept header contents for instances loaded with xf:instance/@src attribute. The 
processor would assume that whatever is returned from that URI should be parsed 
as XML.

In order to load a default instance from a URI that uses content negotiation, 
you could start with an empty/dummy instance, set up a replacing submission 
which has the required accept header specified and trigger that submission once 
the form is initialized.

A more direct approach would be to allow authors to specify content negotiation 
parameters with additional attributes on the xf:instance element. However, this 
would be duplication of facilities already provided in submission. Thus, if the 
use-case can be solved with a custom submission I'd prefer that approach over 
adding syntactic sugar to the xf:instance element.


Philip Fennell wrote:
> I'm working on a XForms demo that combines XML content editing and
> RESTful Web Services.
> Whilst looking at the HTTP request headers sent by an xforms:instance
> request by the Mozilla XForms plug-in I noticed that the server gets the
> same 'Accept' header whether it comes from a hyper-link in the host
> XHTML page or from an XForms instance request:
> <a href="objects/0901047880012b9b" title="example xhtml content"
> type="text/html">...</a>
>  or
> <xforms:instance xmlns="" id="content"
> src="../objects/0901047880012b9b"/>
>  sends
> text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plai
> n;q=0.8,image/png,*/*;q=0.5
> Given that XForms is designed for editing well-formed XML, should it not
> be the case that an XForms implementation should declare to the server
> that it only accepts XML. Now I'd admit that just sending 'text/xml' in
> the 'Accept' header is probably too narrow, but something along these
> lines would allow a server that uses pre-emptive content negotiation to
> return an XML representation of a concept to the XForm and an XHTML
> (preview) representation to a hyper-link from the host XHTML page.
> Otherwise, I cannot see how XForms can operate within a RESTful Web
> Service where content negotiation is used to serve appropriate
> representations from opaque URLs.
> Regards
> Philip Fennell
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Sun Microsystems                Lars Oppermann <lars.oppermann@sun.com>
Nagelsweg 55                    Software Engineer
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http://www.sun.com/             Fax:   +49 40 23646 550
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Received on Friday, 19 October 2007 12:34:29 UTC

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