W3C home > Mailing lists > Public > public-rdf-wg@w3.org > March 2011

Re: Graphs and Being and Time

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 1 Mar 2011 16:59:06 -0600
Cc: RDF WG <public-rdf-wg@w3.org>
Message-Id: <302F2EC7-B1EB-45BF-BFB8-8F9F695A9A78@ihmc.us>
To: David Wood <david.wood@talis.com>

On Mar 1, 2011, at 12:52 PM, David Wood wrote:

> 
> On Mar 1, 2011, at 05:32, Nathan wrote:
> 
>> Hi David,
>> 
>> Sorry, I've realised the below is wrong, so corrected:
>> 
>> Nathan wrote:
>>> 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"?  What is the difference between an "RDF graph token" and a RESTful "representation"?
>>> REST maps a resource to a set of values over time, each single value has a 1:N relationship with representations, "RDF Graph" (the mathematical set, platonic abstraction, g-snap) equates to a single value, and "RDF Graph Token" equates to a representation of that single value.
>> 
>> REST maps a resource to a set of values over time, each single value is a representation, representation equates to "RDF Graph Token" (a chunk of rdf/xml or turtle, a g-text in Sandro's mail).
>> 
>> The g-snap, or abstract graph, isn't a concept which relates to any REST concept, rather it is something specific to our RDF use-cases, in that we have a platonic abstraction, a mathematical set of triples, which we juggle different realizations of (from in memory structures through to serializations and so forth).
>> 
>> So, to re-answer your question, "RDF Graph" is a term we've used to refer to both the abstract set of triples, and the realizations of. The only thing which equates anywhere near a "RESTful resource" in our communities are "Named Graphs" and of course linked data which uses RESTful resources, we GET <u> to retrieve a realization of an abstract set of triples, to get some RDF in some format.
>> 
> 
> 
> Pardon me for saying so, but that doesn't make sense to me.
> 
> A RESTful resource may be anything:  "the intended *conceptual* target of a hypertext reference" was one way Roy Fielding put it (emphasis mine).  There is no reason I can see that an abstract, mathematical concept cannot be a RESTful resource.

I see the opposite. Roy did not always make sense. But he did say, quite clearly and repeatedly, that RESTful resources are functions from times to representations. A mathematical set is not a function from times to anything. So, a mathematical set cannot be a RESTful resource. 

> 
> Andy neatly ducked the question of mapping to a resource:
> 
> On Mar 1, 2011, at 06:30, Andy Seaborne wrote:
>> g-box - place holding a sequence-over-time of values
>> g-snap - one such value
>> g-text - the REST representation.
> 
> 
> Instead, I suggest something like this:
> 
> g-box - a REST resource, over time.
> g-snap - a conception of the REST resource at the time it is addressed.
> g-text - the REST representation.

I'm cool with that, provisionally. I have no idea what "conception of" means here, however. In my vocabulary, a conception of anything is basically a psychological notion. I would vastly prefer to avoid going in that direction. The notion of a mathematical or abstract model is much better defined and less controversial. And we do have to relate whatever we say to the existing RDF specs, which define a graph to be a set (not a conception.) 

Pat


> 
> That seems to address Pat's concern and stays very Webby.
> 
> Regards,
> Dave
> 
> 
> 
>> Apologies, just had to correct myself there.
>> 
>> Best,
>> 
>> Nathan
> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Tuesday, 1 March 2011 22:59:45 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 17:04:03 UTC