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Re: Example for consideration: Resource versus Representation

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 23 Jan 2008 11:51:27 -0600
Message-Id: <p06230902c3bd2caa7d0f@[10.100.0.14]>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
Cc: public-awwsw@w3.org
At 11:34 PM -0500 1/22/08, Alan Ruttenberg wrote:
>Are representations resources?

They can be (anything CAN be a resource....), but its not usually 
very useful to want to treat them as resources, I'd say.

>
>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.

Wrong way to put it. You are making 'representation' into a category, 
but it should be a relationship. That thing you get back is required 
by the REST architecture to be a representation OF the IR. That is, 
whatever we call this thing you get back, it bears a 
webarch:represents relationship to the IR. Saying that doesn't say 
what kind of thing the representation is, only that it represents. So 
we can (using this confusing language we all speak) nominalize this 
and say that it 'is a representation', but that shouldn't be taken to 
mean that this means (or at any rate, that it means usefully) that it 
is a category of Things called Representations.

>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?

Yes.

>If it is, when and how did it become one, having been only a 
>Representation until recently?

When you stored it (in fact when you *created* that file, based on 
the byte stream you got back from the first resource; that byte steam 
being the actual representation of the first IR, if one wants to be 
pedantic.) Being a file, stored stably in a computer, it can possibly 
(see below) be given a URI. However, I see no way to give a URI to a 
byte stream.

>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?

No, because it doesn't know that this file represents anything, so 
such a request is meaningless. But it can still serve the file.

>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.

I think that idea has been floated and rejected by the TAG before. 
Its a resource if it can possibly be given a URI, even if it doesn't 
have one yet.

Pat

>However this statement generated some controversy, so at least this 
>is a point we should resolve.
>
>-Alan


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Received on Wednesday, 23 January 2008 17:52:01 GMT

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