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Re: Example for consideration: Resource versus Representation

From: Tim Berners-Lee <timbl@w3.org>
Date: Wed, 30 Jan 2008 16:41:45 -0500
Cc: public-awwsw@w3.org
Message-Id: <84D75DCC-B5C6-4579-8907-45F40FAFF6BC@w3.org>
To: Alan Ruttenberg <alanruttenberg@gmail.com>


On 2008-01 -22, at 23:34, Alan Ruttenberg wrote:

>
> Are representations resources?
>

Of course, everything is a resource.

> 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.

The Representation is the pair of the response headers and the bits.   
A fleeting thing sent over the wire.

> 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?

We haven't defined 'file' , but on can imagine file being a subset of  
IIR.  can access it using file: URI, or run an HTTP server.

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

*No it wasn't a Representation*.    The bits in the file match the  
bits in the Representation.
a) It isn't a representation - it is related but not the same.
b) It doesn't even faithfully store the representation.

If you to record the details of the representation, you could, in a  
file foo.rdf

<#re1>  headerSet [ http:content-type "Application/pdf" ...]; bits  
"%PDF.....".

the representation would then have a URI foo.rdf#rep. You would be  
being kinda pedantic and breaking levels, which we don't normally do,  
except when we biuld cache metadata in RDF.  (The tabulator does this  
sort of thing internally but hides it unless you ask for it).

So don't do this. The representation is for talking about what happens  
in HTTP and what you can deduce from it.  It is a term in the  
architecture.

Tim
Received on Wednesday, 30 January 2008 21:41:55 GMT

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