Content Negotiated Media Resources -- Clarification Needed

[Andreas Sewe]

Here is an extension of an, IMHO, valid example of using APP. (It builts 
on an example posted by me to <atom-syntax>, [1].) But since I am not 
entirely sure whether it violates the spec (PaceMediaEntries5, to be 
precise) or not, I would like to hear the WG's opinion on it.

So consider the following client/server exchange:

First, the clients posts an image to the collection (at 
<http://example.org/entries>).

    POST /entries HTTP/1.1
    Host: example.org
    Content- Type: image/png
    Content- Length: nnn
    Title: A picture of the beach

    {binary data}

Now the server creates both a media resource of type "image/png" (at 
<http://example.org/media/1.png>) and a media link entry (at 
<http://exmaple.org/entries/1>). But furthermore the server 
automatically converts the media resource to type "image/gif" (made 
available at <http://example.org/media/1.png>).

Finally the media link entry refers to a content-negotiated resource (at 
<http://example.org/media/1>) which makes available both the "image/png" 
and "image/gif" representations. But since the original media resource 
was of type "image/png", only the "image/png" representation is editable 
by the client; the "image/gif" representation obtained by conversion is not.

    HTTP/1.1 201 Created
    Date: Fri, 7 Oct 2005 17:17:11 GMT
    Content- Length: nnn
    Content- Type: application/atom+xml; charset="utf-8"
    Content- Location: http://example.org/entries/1
    Location: http://example.org/entries/1

    <?xml version="1.0"?>
    <entry xmlns="http://www.w3.org/2005/Atom";>
      <title>A picture of the beach</title>
      <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
      <updated>2003-12-13T18:30:02Z</updated>
      <author><name>John Doe</name></author>
      <summary type="text" />
      <!-- editable media link entry -->
      <link rel="edit"
       href="http://example.org/entries/1"; />
      <!-- editable media resource -->
      <link rel="edit-media" type="image/png"
       href="http://example.org/media/1.png"; />
      <link rel="alternate" type="image/png"
       href="http://example.org/media/1.png"; />
      <!-- read-only media resource -->
      <link rel="alternate" type="image/gif"
       href="http://example.org/media/1.gif"; />
      <!-- content negotiated read-only media resource -->
      <content
       src="http://example.org/media/1"; />
    </entry>

Note that there is no content/@type attribute present since the media 
resource (at <http://example.org/media/1>) is content negotiated. This 
violates a SHOULD of RFC 4287, however, which is an issue already 
discussed on <atom-syntax> [1].

But what is worse is the fact that the above at least seems to violate a 
MUST of PaceMediaEntries5:

  The media link entry MUST have a "content" element with a "src"
  attribute which links to the media resource

If you read the above strictly, content/@src is forced to point to the 
non-negotiated media resource of type "image/png" (at 
<http://example.org/media/1.png>; it all depends on what is meant 
exactly by "the media resource"...

So can someone please clarify this, since at least to me the above looks 
like a valid use of both APP and server-driven content negotiation?

With kind regards,

Andreas Sewe

[1] <http://www.imc.org/atom-syntax/mail-archive/msg17708.html>