W3C home > Mailing lists > Public > public-awwsw@w3.org > January 2008

Re: Example for consideration: Resource versus Representation

From: Jonathan Rees <jar@creativecommons.org>
Date: Wed, 23 Jan 2008 10:41:25 -0500
Message-Id: <2407DE26-35F9-457B-B3A7-7C1335B0F99B@creativecommons.org>
To: public-awwsw@w3.org

I think our conversation yesterday got derailed a bit because we  
started using the term "resource" without having first agreed on how  
we wanted to use it.  The confusion reflects the underlying cultural  
gulf that this group needs to bridge - one might call it "knowledge  
engineering meets web architecture".

Let's focus on trying to draw out Noah (and Tim) on the negative  
assertion "a representation is not a Kwyjibo". Negative statements,  
or conditions of potential inconsistency, are always much more  
interesting and informative than positive ones. We just have to  
figure out what the class Kwyjibo is supposed to be.  Noah, did you  
mean one of the following, or yet a new concept?

Kwyjibo =
rfc2616:Resource "A network data object or service"
awww:Resource "An item of interest" ... but, inconsistently, "we do  
not limit the scope of what might be a resource"
rdfs:Resource "The class resource, everything"
rfc3986:Resource   -- "whatever might be identified by a URI" -- says  
that physical objects and abstractions such as numbers "can be"  
resources but doesn't say that they are! -- not a definition since it  
gives no criteria for what things are not permitted to be identified  
by URI.
rest:Resource "temporally varying membership function"
awww:InformationResource - the memorable phrase is "all of their  
essential characteristics can be conveyed in a message"
"web resource" - a term that Noah used yesterday - not sure what it  
means

(I have considered "representation" to be uncontroversial - but I  
could be wrong. It's defined pretty clearly in RFC2616 and nothing in  
AWWW suggests a different sense.)

I think that Alan and I use 'resource' in the RDFS sense, which we  
had always thought was consistent with AWWW. By this definition a  
resource doesn't have to have been given a name by anyone - for  
example every particle in the universe is, and always has been, a  
resource. So any representation, named or otherwise, is a resource  
(rdfs:Resource).
Clearly the class Kwyjibo that representations are supposed to not  
belong to is not this ultimately comprehensive class (i.e. no one  
argues that a representation is not an rdfs:Resource).

Tim has mysteriously stated that the class Representation is disjoint  
with the class InformationResource (Kwyjibo = InformationResource).  
This cannot be inferred from AWWW, which is why it's so interesting.  
There seem to be important architectural principles not articulated  
in AWWW, and these need to be surfaced so that they can be discussed  
openly and followed properly.

A considerably weaker statement would be that some (or most)  
representations don't have URIs. This may be empirically true  
(although someone could in principle schematically give every  
representation a URI in one fell swoop,, making it false - perhaps as  
we speak someone has already done this) but doesn't help us to get  
any class disjointness of the sort that would be helpful in nailing  
down the architecture.

Jonathan


On Jan 22, 2008, at 11:34 PM, Alan Ruttenberg wrote:

> Are representations resources?
>
> I have heard the argument that they are not. In this morning's call  
> I agreed to send an example I've been thinking about.
>
> Consider some Information Resource that responds to a request with  
> a Representation of type application/pdf. I save the response on my  
> hard disk. Is the thing I have (henceforth known as the file)  on  
> my hard disk an Information Resource? If it is, when and how did it  
> become one, having been only a Representation until recently? If  
> not, what happens when I move the file to a directory (actually, I  
> don't move the file, I make changes to directory structures) that  
> my Apache server can serve from. Can my server respond to requests  
> for Representations? If not, how should it avoid serving this file?  
> If the server answers requests only about Resources and is willing  
> to serve the file then the file must be a Resource. If it is, same  
> question: When and how did it become a Resource, having only  
> recently been a Representation?
>
> It was suggested that perhaps Resources were only Resources if they  
> were identified by a URI. However this statement generated some  
> controversy, so at least this is a point we should resolve.
>
> -Alan
>
>
Received on Wednesday, 23 January 2008 15:41:44 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 July 2008 07:55:27 GMT