Thanks for the useful feedback Cyril! :-)
There has been quite some discussion both here on the mailing list, in F2Fs and also on the IRC about the use of headers. In fact, I think what you raise here is quite a good summary of those discussions that were had. Using the OCCI text syntax within the header, from my POV, is now largely historical and for the those related comments I can't disagree. What should be noted is that the HTTP rendering spec details how a text-based syntax can be relayed between client and service. It does note that the content can be in the header but the default is in the body. 

To other aspects - yes filtering in my view is simple and there has been talk about making it a little more encompassing (e.g. addition of logical operators). The origins of actions are from this detailed conversation [1] over on Tim Bray's blog. We'd love to know more about any reservations about the linking scheme. Also do you see anything that could be brought to the spec to improve it?

Regards,

Andy
andy.edmonds.be

[1] http://www.tbray.org/ongoing/When/200x/2009/03/20/Rest-Casuistry


On Mon, Jul 11, 2011 at 10:32, Cyril Rohr <contact@crohr.me> wrote:
Hi Andy, all,

It's hard to be constructive in 140 characters, so thanks for letting me
elaborate on this list.

My concerns are related to the "RESTful HTTP Rendering" spec [1], which views
HTTP headers as the primary mean of transferring resource representations
between a user-agent and an OCCI server. I can see how you you may have ended
there (no need to define a media type, "universality" of the HTTP protocol,
new RFC drafts about `Category` [4] and `Link` [5] headers popping up, etc.),
but that just looks wrong to me for the following reasons:

* The most obvious, and a point that you raise in the spec [1], is that the
  HTTP header max size is often limited by intermediaries (for instance,
  default limit on Squid is 20KB [2]), while body max size is not. The spec
  warns:

  "Space in the HTTP header section of a HTTP request is a limited resource.
  By this, it is noted that many HTTP servers limit the number of bytes that
  can be placed in the HTTP Header area. Implementers MUST be aware of this
  limitation in their own implementation and take appropriate measures so that
  truncation of header data does NOT occur."

  You can't assume that there won't be intermediaries between the user-agent
  and the server (proxies, caches, etc.), therefore I don't see how an
  implementer can do anything about the header size limit, which means it is
  safe to assume that the HTTP Rendering via `text/occi` is broken (unless you
  have already thought about a possible solution, in which case it should be
  included in the spec). You can't even use the `Content-MD5` [3] header to
  provide an end-to-end message integrity check. And the message header is not
  compressible, contrary to the message body.

* More generally, methods and headers are there to indicate the purpose of a
  request, not the resource representation itself.

* Finally, you define a `text/occi` content-type, which looks like an empty
  shell. I mean, if I understand correctly, the only payload you'll ever have
  is "OK" on successful operations. AFAIK, a media type definition [6] is
  mainly about the structure and semantics of the message body. It's not about
  defining custom HTTP headers to replace the message body.

I also have some concerns about the filtering mechanism, linking mechanism and
the way you define actions, but if I had to sum up my position it would be
that I have the feeling that you went extreme with the REST concept, and tried
to put in the spec as much novelty (in terms of recent HTTP-related
specs/drafts) as you could. Nothing wrong with that, but the result is
somewhat convoluted. Also, the decision to put everything in the header part
of the message renders a lot of standard HTTP header fields useless.

I appreciate the effort and time it takes to build a spec like this. From a
standardization body though, I would have expected that you properly define a
new media type for the rendering, not custom header extensions. I recall a
(now dead?) XHTML based rendering doc, which had some flaws but was going more
in that direction. I can see that you plan on specifying new content types in
the future: I think it would be good to shift the attention back to the body.

Thank you for your time.
Best Regards,

Cyril
--


On 8 Jul 2011, at 18:03, Andy Edmonds wrote:

Hey Cyril,
I saw some of your comments [1] [2] on twitter about OCCI. It'd be great if you could elaborate on them on the list as everyone here really values useful and constructive comments and critique.

BTW: you might have been viewing older OCCI specs. The latest published are here [3].

Cheers,