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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 09:27:12 -0400
Message-ID: <505876B0.10406@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 09:12 AM, Sandro Hawke wrote:
> On 09/18/2012 09:05 AM, Peter F. Patel-Schneider wrote:
>>
>> On 09/17/2012 04:46 PM, Sandro Hawke wrote:
>>> On 09/17/2012 02:02 PM, Peter F. Patel-Schneider wrote:
>>>
>> [...]
>>>
>>> Can you be a little more specific, and tell a story about something 
>>> specific someone is likely to want to do that they could do with your 
>>> proposed semantics and not with the proposal on the agenda?
>>>
>>> (The two things I see are: (1) the default graph being "asserted", which 
>>> seems easy enough to work around if desired [just use a named graph], and 
>>> (2) URIs being interpreted the same way throughout the dataset... but I 
>>> can't see what harm that could cause.   Maybe I'm on the wrong track.  
>>> Okay, I'm also concerned about unwanted-but-valid inference being done, 
>>> but that's an issue throughout RDF, not just about datasets.)
>>>
>>>       -- Sandro
>>>
>>
>> (2) I don't know where in the minimal semantics there is a notion that IRIs 
>> have to be interpreted the same way throughout the dataset, so I don't see 
>> any difference here.  If, however, there is a need to interpret IRIs the 
>> same way throughout a dataset then this would indeed be a vast difference, 
>> essentially requiring rigid designators in datasets.   This would mean that 
>> any equality assertion in the default graph would carry over into the named 
>> graphs (and maybe vice versa).
>>
>
> 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?

>> (1) Even if you used an empty default graph, you get some carry-over into 
>> the named graphs.   For example, the named graph resources can only be 
>> taken from the resources in this interpretation. Fortunately (or 
>> unfortunately) all RDF interpretations are infinite, so there probably are 
>> no observable consequences.
>>
>> But in any case, why should I be forced into turning my default graph into 
>> a named graph (with some arbitrary name) and adding an empty default graph?
>>
>>
>> One interesting use of RDF datasets is to collect information from the 
>> web.   The named graphs record the source of the graphs and their 
>> contents.  The default graph can either be related to these collected 
>> graphs or unrelated to them.  Having the default graph affect the meaning 
>> of the named graphs is undesired.
>>
>
> I don't see how you can usefully communicate collected information like that 
> unless you have a private protocol arranged (in which case this is all 
> moot), or you use the default graph for metadata.
>
>        -- Sandro
>

I would turn this question around and ask how the current minimal semantics 
can be used for the same purpose.

I also don't see why excluding useful private ways of doing things 
(particularly ones that might already be in use) is moot.

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.

peter
Received on Tuesday, 18 September 2012 13:27:52 GMT

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