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Re: Labelled graphs

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 25 Apr 2012 14:06:39 +0100
Message-ID: <4F97F6DF.3020200@epimorphics.com>
To: Sandro Hawke <sandro@w3.org>
CC: Ivan Herman <ivan@w3.org>, public-rdf-wg@w3.org


On 25/04/12 13:46, Sandro Hawke wrote:
> On Wed, 2012-04-25 at 13:11 +0100, Andy Seaborne wrote:
>>
>> On 25/04/12 12:28, Ivan Herman wrote:
>>>
>>> On Apr 25, 2012, at 05:16 , Sandro Hawke wrote:
>>>
>>>> On Tue, 2012-04-24 at 16:05 +0100, Andy Seaborne wrote:
>>>>>
>>>>> On 24/04/12 13:04, Sandro Hawke wrote:
>>>>>> (mostly agreement, a few details)
>>>>>>
>>>>>> On Tue, 2012-04-24 at 12:03 +0100, Andy Seaborne wrote:
>>>>>>>
>>>>>>> On 17/04/12 16:59, Guus Schreiber wrote:
>>>>>>> ...
>>>>>>>
>>>>>>>> An attempt at formulating a possible conclusion/consensus from this thread:
>>>>>>>>
>>>>>>>> * Non-typed labels are simply associations, no special semantics
>>>>>>
>>>>>> There are some semantics, though: the label IRI (or blank node) denotes
>>>>>> something (maybe call it a "labeling object"), and that something is
>>>>>> associated with the graph.
>>>>>
>>>>> Given the "something" indirection, whether that counts as "semantics" or
>>>>> not is a bit moot to me.  It's "no fixed semantics".
>>>>
>>>> Here's the part that's important to me:
>>>>
>>>>          Under OWL entailment and our dataset semantics, does
>>>>             {<u1>   owl:sameAs<u2>   }
>>>>             <u1>   {<a>   <b>   <c>   }
>>>>          entail
>>>>             <u2>   {<a>   <b>   <c>   }
>>>>          ?
>>>>
>>>
>>> FWIW, in the case of http://www.w3.org/2011/rdf-wg/wiki/Graphs_Design_6.1/Sem the answer is clearly yes.
>>
>> I think this is at a different level.
>>
>> (I think that) the most basic thing we (this WG) needs to do is define
>> syntax so that things do not go wrong.  This does not need to fix the
>> semantics for all time.
>
> To be clear, are you saying you would like the entirety of this WG's
> output concerning "named graphs" to be a Recommendation for the grammar
> of TriG?

No.  I'm suggesting we must at least provide that.  It would be a step 
forward.

Given the discussions, I am not convinced that fixing one semantics is 
desirable.  I see different viewpoints, from different use cases, all of 
which have merit.  Deciding the semantics now feels like research, there 
not being one as input.

I think the best approach is to define the absolute minimum, and publish 
the semantics as based on that.  This means if the semantic proposals 
are found wanting (not in a technical sense, but in a utility sense c.f. 
reification) others can also emerge.

This isn't giving up - it's realising there is a minimum and 
possibilities on top of the core basics.

 > I note that our charter says:
 >
 >          Required features
 >                * Standardize a model and semantics for multiple graphs
 >                  and graphs stores

My conclusion currently is that there are different ways of using named 
graphs in applications and they are all valuable.  The use cases are not 
met by some common semantics choice directly.

Even if they can all be built on one common semantics (and this itself 
is not obvious to me - I can see different strands still running), it 
can still end up too complicated in practice.  So we can meet the letter 
of the charter and still not improve the situation.

And there are other things in the charter.

	Andy
Received on Wednesday, 25 April 2012 13:07:19 UTC

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