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

From: Guus Schreiber <guus.schreiber@vu.nl>
Date: Wed, 14 Dec 2011 17:54:45 +0100
Message-ID: <4EE8D4D5.1090003@vu.nl>
To: RDF WG <public-rdf-wg@w3.org>


-------- Original Message --------
Subject: graphs and documents Re: [ALL] agenda telecon 14 Dec
Date: Tue, 13 Dec 2011 22:59:59 -0500
From: Tim Berners-Lee <timbl@w3.org>
To: Pat Hayes <phayes@ihmc.us>
CC: David Wood <david@3roundstones.com>, Guus Schreiber 
<guus.schreiber@vu.nl>, RDF WG <public-rdf-wg@w3.org>

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 16:55:21 GMT

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