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Re: different Semantics proposals (Re: Agenda for 19 Sep 2012)

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Tue, 18 Sep 2012 12:00:40 -0400
Message-ID: <50589AA8.8080803@gmail.com>
To: Sandro Hawke <sandro@w3.org>
CC: David Wood <david@3roundstones.com>, "public-rdf-wg@w3.org Group WG" <public-rdf-wg@w3.org>

On 09/18/2012 10:40 AM, Sandro Hawke wrote:
> On 09/18/2012 09:27 AM, Peter F. Patel-Schneider wrote:
>>
>> On 09/18/2012 09:12 AM, Sandro Hawke wrote:
>>> On 09/18/2012 09:05 AM, Peter F. Patel-Schneider wrote:
>>>>
>>>>
[...]
>>>
>>> Sorry, I just meant the IRIs of the named graphs, the n's in the <n,g> 
>>> pairs, being interpreted the same as IRIs the default graph.
>>
>> OK, so you are referring to the part of the semantics where it is the 
>> denotation of the graph names in the default graph that is used as the 
>> start of the mapping to the named graph itself. I am against this because 
>> there can be strange bleeding from the default graph to the identity of the 
>> named graphs, such as in example 2.16 in 
>> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Minimal-dataset-semantics
>> although the analysis there is incorrect.
>>
>> if all you are dong is recording named graphs, then why should information 
>> in the default graph potentially cause two named graphs to be smushed 
>> together?
>>
>
> How could it not?
>
> If I know
>   <g1> { ... }
>   <g2> { ... }
>
> and if I know, because of some metadata, that g1 and g2 are actually the 
> same thing, doesn't that imply some kind of smushing or inconsistency?

Only if you also want the denotations of the graph names to carry meaning 
related to the named graphs.  I don't see that this is necessary the case.

[...]

>
> [...] The one thing I can argue for, I think, is that the graph names be 
> strongly connected to those same names being used in the default graph.   
> For example, I think we need to be able to say things like this:
>
>     <http://example.org/d1> { <a> <b> 1 }.
>     <http://example.org/d1> eg1:lastModified "Wed, 12 Sep 2012 11:42:31 GMT".
>
>
> where eg1:lastModified is defined such that this dataset conveys the 
> knowledge that (1) a dereference on URL "http://example.org/d1" was done; 
> (2) it resulted in (at least?) the triple
> { <a> <b> 1 }; and (3) the HTTP Last-Modified header returned during that 
> dereference was the string "Wed, 12 Sep 2012 11:42:31 GMT".

Yes, one might want to say that.  However, where in this is there a need for 
the IRI to denote the graph?

Further, the minimal semantics doesn't support this well, as its semantics 
doesn't relate names to actual RDF graphs, only to equivalence classes of RDF 
graphs.

[...]


>
>> I also don't see why excluding useful private ways of doing things 
>> (particularly ones that might already be in use) is moot.
>>
>
> Well, I think these standards only apply between systems, not within 
> systems.  Private communications are essentially system-internals, and none 
> of our business.  Right?

Correct, but if the semantics for RDF datasets rules out some useful private 
methods then that's not good.

>
>> I didn't exclude using the default graph to record information about the 
>> named graphs and their sources.  However, I didn't want information in the 
>> default graph to affect the situation in the named graphs.
>>
>
> My concern/motivation is in my example above.   The semantics need to be 
> strong enough that eg1:lastModified can be defined to make my example 
> dataset mean to consumers what the producer wants it to mean.
>
> I leave any argument for more powerful semantics to others, who have other 
> use cases in mind.
>
>      -- Sandro

I still don't know what the minimal semantics has to support this use.  If you 
really want this then don't you need a theory of web retrieval and something 
in the semantics stating that named graphs are the result of this retrieval?

peter
Received on Tuesday, 18 September 2012 16:01:13 GMT

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