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FW: Http.ow and jar-diagram-7.pdf l (was RE: JAR conflict for July 7 AWWSW telecon)

From: Williams, Stuart (HP Labs, Bristol) <skw@hp.com>
Date: Mon, 6 Jul 2009 13:55:38 +0000
To: Jonathan Rees <jar@creativecommons.org>
CC: AWWSW TF <public-awwsw@w3.org>
Message-ID: <233101CD2D78D64E8C6691E90030E5C832D33A651E@GVW1120EXC.americas.hpqcorp.net>
[Apologies accidentally hit the send button before...]

Hello Jonathan,

> I would still really like to get feedback on
> http://w3.org/2001/tag/awwsw/http.owl
> and
> http://w3.org/2001/tag/awwsw/jar-diagram-7.pdf

The one relation that I can't make sense of (yet) in http.owl is "http:ofWaRepresentation" the associated comment says:

	"C hasWaRepresentation R when R is the wa-representation that corresponds to the resource in which C inheres during C's lifetime."

which seems to be a comment about a different relation... Or at least has not kept up with some name changes. Domain and range of "ofWaRepresentation" are "http:Message" and "http:Entity" respectively which has left me confused about the intent of the relation.

Jar-diagram-7.pdf shows the same relation as having a domain of "Correspondence" and a range of WaRepresentation. This makes way more sense than it does in http.owl... Ie. There is a correspondence between the WaRepresentation and a Rfc2616Resource (Get200Candidate) evidenced by a message exchange which conveys the WaRepresentation.

--

Re rdfs:comment on http://w3.org/2001/tag/awwsw/http#WaRepresentation ie.

<quote>
This is meant to capture the web architecture definition of 'representation', which is a problem because there isn't complete agreement on what this is.

AWWW has "Data that encodes information about resource state" but this does not necessarily mesh well with HTTP, which does not require either that the resource has state or that a 200 entity encodes information about state when it exists.

HTTP has "An entity included with a response that is subject to content negotiation, as described in section 12. There may exist multiple representations associated with a particular response status."  We also find (at least in HTTPbis) "Any response containing an entity-body MAY be subject to negotiation, including error responses." I guess it's up to the server, and the entity/representation distinction is not operational.

Some people (e.g. Harry) have suggested that representations *cannot* be persistent (stored) - that they are "on the wire" only. I don't see this being supported by either definition.

I'm hoping we'll be able to come up with a consensus definition that bends each of these enough to harmonize them - or else that we decide we don't need this class at all for a treatment of HTTP.
</quote>

I think this is a comment about a type/token distinction for WaRepresentations and when two distinct messages convey the same representation. One view is that they simply can't because two distinct messages must occupy a different region of space/time. The other view is that as long as they convey bytewise identical content they convey the same representation. Somewhere in between, somewhat more coarse grained than the first of the position above and more fine grained than the second is to identify a representation by it's bit/byte sequence (inc media type) and last-modified time/date. This is then reflective (or should be) of when the server first emitted the representation in response to a question - and respects the repetion induced either by multple agents asking (effecitively) the same question and being served the 'same' answer be it directly from the origin server or a cached copy from a proxy. 

[However, beware transcoding proxies and local ad insertions - which may change representions without reference to their origin server]

Summary: Suggest WaRepresentation identified by (bytesequence)x(media-type)x(last-modifed date/time) - there's a role for OWL 2 compound keys :-)

--

http:Entity

This a strange one... http:Entity are encapuslated in http:Messages ie. They are a *partOf* an http:Message. What they carry may be *partOf* a WaRepresentation (amongst other things). In that respect I can't really see an http:Entity as rdf:subClassOf http:WaRepresentation.  [I may be confusuing message body with entity - I'm thinking of chunked situations where an http:Message conveys less than a full WaRepresentation].

--

Jar-diagram-07.pdf includes a (tentative?) notion of a process. I think that process may serve to surface 'evidence' of correspondences in the form of http interactions, but with a god-like eye such correspondences exist whether or not the action of a client cause them to be exposed. Hmmmm... but what about the actions of a published that publishes the resource - without their actions the correspondence certainly could not be observed - and may not exists at all. Hmmmm....

Maybe the "Exchange" in har-diagram-7.pdf is induced by the process shown therein (the process being part of the behaviour of a "Client"?); likewise for http.owl although process is currently absent from the file.

--

In http.owl:

I find the little clutch of http:Get200Candidate subClasses (transitively) confusuing - I'm a little lost about the intent of each and the distinctions between them

HTH

Stuart
--


> -----Original Message-----
> From: Jonathan Rees [mailto:jar@creativecommons.org] 
> Sent: 06 July 2009 12:12
> To: Williams, Stuart (HP Labs, Bristol)
> Cc: AWWSW TF
> Subject: Re: JAR conflict for July 7 AWWSW telecon
> 
> On Mon, Jul 6, 2009 at 5:13 AM, Williams, Stuart (HP Labs,
> Bristol)<skw@hp.com> wrote:
> > I too have a conflict and cannot make the call on 7th July.
> 
> OK, it looks as if 7 July is canceled.
> 
> I would still really like to get feedback on
> http://w3.org/2001/tag/awwsw/http.owl
> and
> http://w3.org/2001/tag/awwsw/jar-diagram-7.pdf
> 
> but I don't know if it's worth scheduling an extra call. Let's try
> email, and I'll meet with Alan R in person about it.
> 
> I want to start thinking soon about what should be in a report on this
> effort. Not that the work is anywhere near done, but I hope each of
> you (active participants) will think about what would be good content
> and structure, to help guide next steps.
> 
> Jonathan
Received on Monday, 6 July 2009 13:57:26 GMT

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