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Re: Graphs and Being and Time

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 1 Mar 2011 12:44:00 -0600
Message-Id: <FB9F02DC-D6E4-484C-88A1-729C9D103567@ihmc.us>
To: RDF WG <public-rdf-wg@w3.org>

On Feb 28, 2011, at 1:42 PM, David Wood wrote:

> On Feb 24, 2011, at 13:12, Pat Hayes wrote:
> 
>> It is much simpler: it is just wanting the WG to acknowledge that "an RDF graph" can either be a mathematical set, or it can be some kind of document or data structure or file than can be transmitted over a computer network. But it can't be both.
> 
> What is the difference between an "RDF graph" and a RESTful "resource"?  

(Following definitions in existing specifications and discussions...) 

An RDF graph is a set, in the mathematical sense. This is a pure-mathematical abstraction, AKA a Platonic abstraction. A RESTful resource, as I understand it, is something that can be 'poked' with an HTTP (or other XXTP) request and when so poked will emit a "representation" of itself. I use scare quotes because exactly what this word means here has been the topic of much, um, discussion. But whatever it means, it is quite certain that emitting a representation of any kind is not something that a set could do, because sets can't DO anything. (And even if they could, they would do the same thing every time, whereas a REST resource is a thing with state, which can do different things every time, eg a clock.)

> What is the difference between an "RDF graph token" and a RESTful "representation"?

Well, a graph can have all kinds of tokens, to be strict, eg you can draw a picture of one on a piece of paper. But the kind I was talking about could be a RESTful resource, which was the main point. So whats the difference between a RESTful resource and a RESTful representation? Again, as I understand it, the key difference is that the first has a state - its like a g-box - whereas the second doesn't - its like a g-text (of the g-snap which is the abstraction defining the state of the g-box, if I have Sandro's terminology right.) 

Now, I admit that it would be perfectly correct to call a g-text a graph token as well. Sandro has made a further distinction that I wasn't trying to tackle, between the instantaneous 'graph state' of a g-box and the serialization of this graph that gets sent when you poke it with a transfer protocol prompt. Speaking purely from an abstract conceptual model point of view there isn't much to choose between these, but when we get into Web architecture it is a rather important distinction. 

Pat

> 
> Regards,
> Dave
> 
> 
> 
> 

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Received on Tuesday, 1 March 2011 18:44:37 UTC

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