Re: Is an XForm an application for, or a representation of an instance data?

On Jul 22, 2011, at 10:26 AM, Philip Fennell wrote:

> This is good philosophical stuff but with a practical edge to it:
> =20
> With regard to XForms and RESTful Web Services, a favourite =
hobby-horse of mine, I was answering a question on the xsltforms-support =
mailing list about setting the Accept header for submissions and =
commented upon a solution that used the same URI to retrieve either the =
XML representation of the resource or an XForm that referenced the =
resource. The Accept header was used, via content negotiation, to =
indicate which representation was required. The implication is that if =
you use the same URI then the XForm must be regarded as another =
representation of the resource pointed to by the URI.
> =20
> My questions are:
> =20
> 1) If you embed an instance data document inside an XForm that =
provides a view of the document=92s content, can the resulting XForms =
document be thought of as a representation of the instance data?

There is a sense in which this question appears to be one of human =
psychology.
Is it possible for someone to think of a form to edit X as being a =
representation of
X?  That's an empirical question to which the answer is pretty clearly =
'yes'.

Is it a reasonable way of thinking?  Is it, in particular, consistent =
with the way
Web architecture defines 'resource'?

As far as I can tell, Web architecture does not define 'resource' at =
all, and
all the discussions of Web architecture I've seen clearly prefer to risk=20=

obscurity and confusion rather than risk unintentionally limiting what =
can be
thought of as a resource.

So as far as I can see, speaking only for myself, yes, it's perfectly =
consistent
with Web architecture, both in the sense of not contradicting it (there =
not being
much to contradict) and in the sense of appearing to be a perfectly =
legitimate
exercise of the resource owner's responsibility to decide what a =
resource is
and what counts as a representation of it.=20

I think it's also consistent with Web architecture to decide to give X =
and a form
to edit X different URIs -- the resource owner appears to be the one who =
has=20
the right and responsibility to decide.

>  2) If the answer to the (1) is 'yes', then does that still hold true =
when the instance document is no longer embedded, in-line, but is =
included by URI reference instead?

I think so.  Or perhaps I should say I think it should:  making a =
question of
resource identity depend on whether certain content is inline or present =
by
reference seems to place more weight on network location than is a good
idea.

> =20
> 3) If you=92re happy that the answers to (1) and (2) are 'yes' then, =
given that both the XML representation of the resource and the XForm =
representation of the resource are nominally application/xml but the =
later could be application/xhtml+xml, how would you use content =
negotiation to differentiate between the two requests? You have to take =
into account the fact that different XForms implementations require =
different response content-types in order that the form will be =
processed correctly and also you cannot rule-out that a plain =
application/xhtml+xml (XHTML) representation may also be required.

Really good question, to which I for one don't have a good answer.  Some
very smart people I know have told me content negotiation is the right =
answer
for a lot of things, so my instinct is to say it sounds promising.  But =
(a) they
have also complained bitterly that conneg is not well implemented or
understood, so I have never been sure it was possible to make it work =
without
more effort than normal humans can expect to expend, and (b) there is
always the possibility that conneg appears to be the right answer only =
because
one cannot currently use it very well, and that concrete experience =
using it=20
will reveal that it works well as an answer for some things and not for =
others.


>  =20
> The ability to request a representation of a resource that allows the =
resource to be edited is an interesting one and I=92m not sure it has =
been covered in any great detail if at all.

Agreed on both counts.

> Is the editing application a resource in its own right or a =
representation of the resource.

That's a Web Architecture koan if I've ever seen one.

> It=92s all rather relative and seems to revolve around whether you see =
the user accessing the resource to edit it or they access an editing =
application (the XForm) that retrieves the resource.

I think I agree.

> I=92d be interested in your opinions.
> =20

For what it's worth, then, here they are.

best,

Michael Sperberg-McQueen


--=20
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