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Re: graphs and documents Re: [ALL] agenda telecon 14 Dec

From: David Wood <david@3roundstones.com>
Date: Wed, 14 Dec 2011 11:08:41 -0500
Cc: Pat Hayes <phayes@ihmc.us>, Guus Schreiber <guus.schreiber@vu.nl>, RDF WG <public-rdf-wg@w3.org>
Message-Id: <4FE1AF68-44B1-4CD0-A874-52038496385B@3roundstones.com>
To: Tim Berners-Lee <timbl@w3.org>
OK, I give up and now back Richard's RDF Dataset proposal in lieu of this discussion.

Tim lost me when he said that a document returned from a URI resolution does not equal a RESTful Representation.  Also, we have continued confusion in this thread about what a "graph" is - see my earlier objection to the continuing use of the term RDF Graph for a g-snap.

Regards,
Dave




On Dec 13, 2011, at 22:59, Tim Berners-Lee wrote:

> I'm afraid I must correct this.
> Apologies to those who have heard my definitions many times.
> 
> On 2011-12 -13, at 20:36, Pat Hayes wrote:
> 
>> 
>> On Dec 13, 2011, at 5:29 PM, David Wood wrote:
>> 
>>> Hi all,
>>> 
>>> I had a lengthy conversation with TimBL about named graphs at the LEDP Workshop [1] last week.  Briefly, he feels that the semantics for named graphs should work like this:
>>> 
>>> - An RDF Graph is named via a URI.
>> 
>> OK so far...
> 
> Well, actually the URI denotes a document, but there is a 1:1 relationship (log:semantics)
> mostly between documents and graphs here.
> 
> The same URIs can be used I think in SPARQL after the "GRAPH" keyword
> because the GRAPH keyword uses the document's URI to
> indicate which graph.
> 
> In my language,  (1 2) is a list,  { ex:s ex:p ex:o }  is a graph, "foo bar" is a string, and 3.14159 is
> a number and I don't  say that URIs formally denote any of those immutable data values.
> 
> You can say
> 
> 	 ex:pi  =  3.145926                  
> 
> which means that whatever ex:pi denotes it is equal to 3.145926.
> (Now, for systems which understand =, this means they can use ex:pi
> most places instead of  3.145926 in mathematical formuale
> and so in fact can treat ex:pi as denoting 3.1415926,
> even though in the basic RDF graph language, ex:pi doesn't denote
> 3.1415926.)
> 
> and you can say 
> 
> 	<#g1> =  {  ex:s ex:p ex:o }
> 
> which you can read loosely as "in this document we use local symbol
> g1 to denote [something which is equal to] the graph {  ex:s ex:p ex:o }.
> 
> I would NOT say
> 
> 	<> =  {  ex:s ex:p ex:o }                                       X NO
> 
> because <> is this document and  {  ex:s ex:p ex:o } is a graph,
> nor would I say 
> 
> 	<http://www.w3.org/2011/12/13-foo.n3> =  {  ex:s ex:p ex:o } .           X NO
> 
> I would say
> 
> 	<http://www.w3.org/2011/12/13-foo.n3> log:semantics {  ex:s ex:p ex:o } .  
> 
> where log:semantics is the relationship between a document
> and the n3 graph whose meaning is the meaning of the document
> and which on a good day you can get by looking up the document
> on the web and parsing which you get back. 
> 
> 
>> 
>>> - The URI denotes the RESTful Representation that is returned when the URI is resolved.
> 
> No it doesn't, it denotes the document. 
> 
>>> 
>>> That is, the URI denotes the graph's contents, not the graph Resource itself.
> 
> Eh? Maybe you are using the word "graph" like I use "document".
> I don't find that helpful.
> 
>> 
>> I don't understand what that means. What is the content of a graph?
> 
> exactly.
> 
>> But in any case, doesnt that directly contradict the previous sentence? 
>> 
>> But whatever, it seems very odd for TimBL to advocate that an IRI not denote a resource. Are you *sure* you have this right? 
> 
> Good catch Pat.
> 
>> 
>>> 
>>> How do Peter and Pat feel about that?
>>> 
>>> TimBL: Please let us know if I misrepresented your position.
> 
> You did.
> 
>>> 
>>> Separately, Elsevier representatives Brad Allen and Alan Yagoda informed me that by "named graphs" they mean an RDF Graph that is referenced by a URI.
>> 
> 
> I suspect that if you ask them whether they are happy to use that URI for a web document
> and indirectly use it to identify the graph by implication, I suspect they would be OK with that.
> 
> 
>> Right, that is what the term was defined to mean in the paper which introduced the terminology in the first place. 
>> 
>>> Resolution of that URI returns the graph contents (a g-text) via RESTful interaction.
> 
> That would make sense to me if you say
> 
> 	Resolution of that URI returns the document contents (a g-text) via RESTful interaction.
> 
>> 
>> No, that simply does not make sense. Graphs do not have contents and do not interact RESTfully or otherwise. Graphs are mathematical abstractions, remember?
> 
> Yes
> 
>> An RDF graph is a *set* of triples.... 
>> 
> 
> Yes
> 
>> Maybe if you can say what you mean using the terminology we have all agreed upon, I might be able to figure out what you are saying. 
>> 
>> Pat
>> 
>>> That would seem to be in line with TimBL's preference.
>>> 
>>> Regards,
>>> Dave
> 
Received on Wednesday, 14 December 2011 16:09:39 GMT

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