Another definition of representation, from Pat

From: http://www.w3.org/mid/E5B9401C-8E18-47A5-9A46-099F6B24E05A@ihmc.us

---------- Forwarded message ----------
From: Pat Hayes <phayes@ihmc.us>
Date: Wed, Jul 15, 2009 at 4:38 PM
Subject: Re: Review of new HTTPbis text for 303 See Other
To: Xiaoshu Wang <xiao@renci.org>
Cc: Richard Cyganiak <richard@cyganiak.de>, "Roy T. Fielding" <
fielding@gbiv.com>, Jonathan Rees <jar@creativecommons.org>, Julian Reschke
<julian.reschke@gmx.de>, HTTP Working Group <ietf-http-wg@w3.org>,
www-tag@w3.org


But I didn't ask about getting a representation in a broad sense, but in the
very narrow sense used in awww debates, where it means the kind of
'representation' which Roy talks about in his thesis REST model, and which
HTTP talks about when it refers to representations of resources. This much
narrower sense refers to *a byte stream which is a sufficiently detailed and
precise representation as to allow a close-to-identical copy of the resource
to be assembled by the recipient of the message.* For example, this kind of
representation of a page of a book might be a high-resolution image of the
page, or it might be a PDF file which can be reconstructed into an accurate
digital rendering of the original page. But a mere description in RDF, for
example, would not meet these very tight requirements on
awww:representations. Seems to me that to do this with hamburgers requires a
matter transporter or telekinesis.

If you've been following the thread, one of the things I was thinking about
recently was where else in the http spec are semantics implied (the extreme
view Masinter/Cyganiak: Nowhere). The place I was thinking about was the
qvalues for content negotiation.

Are any of the definitions we've come up with for representation such that
they allow for this kind of
ordering (i.e. their nature, as explained in their definition, make clear
that they are the sort of things that can be ordered by quality or relative
degradation)

-Alan

3.9 Quality Values

   HTTP content negotiation (section 12) uses short "floating point"
   numbers to indicate the relative importance ("weight") of various
   negotiable parameters.  A weight is normalized to a real number in
   the range 0 through 1, where 0 is the minimum and 1 the maximum
   value. If a parameter has a quality value of 0, then content with
   this parameter is `not acceptable' for the client. HTTP/1.1
   applications MUST NOT generate more than three digits after the
   decimal point. User configuration of these values SHOULD also be
   limited in this fashion.

       qvalue         = ( "0" [ "." 0*3DIGIT ] )
                      | ( "1" [ "." 0*3("0") ] )

   "Quality values" is a misnomer, since these values merely represent
   relative degradation in desired quality.