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Re: Minimal dataset semantics

From: Ivan Herman <ivan@w3.org>
Date: Thu, 23 Aug 2012 17:23:32 +0200
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <8D52381E-7696-4957-8586-B3F1BA7DB262@w3.org>
To: Richard Cyganiak <richard@cyganiak.de>
Richard,

the text says:

[[[
The interpretation of an RDF dataset is the interpretation of its default graph. The presence or absence of named graphs does not affect the truth of a dataset.
]]]

whether the mathematical formalism reflects that or not is secondary; if it does not, than it is wrong.

That being said, I presume you refer to the entry in the formalism that says 

∀i,j, i,j=1,…,n: if ui = uj then Gi and Gj are equal.

but it also says: 

[[[
In this section the “equality” of graphs in a dataset means that they are mutually inferable through simple entailment.
]]]

So yes, the current quoting semantics does not do your entry (b) below, but I am not sure I understand your statement about the contradiction.

But all that may be moot with the recent proposals of Antoine, so this issue may be overran by events.

Ivan


On Aug 23, 2012, at 17:06 , Richard Cyganiak wrote:

> If we define a semantics for datasets at all, it should be such that:
> 
> 1. It formalizes what is denoted by graph IRIs
> 2. Interesting semantic extensions can be made by third parties or future WG
> 3. It doesn't preclude any reasonable semantic extensions
> 
> The problem with the quoting semantics is that it fails #3. The quoting semantics makes it a contradiction if dataset A and dataset B contain the same graph IRI with different associated graphs. We cannot do semantic extensions that produce useful additional entailments from a contradiction.
> 
> No other proposed semantics does have that problem. All of the other proposed semantics can be easily extended with an additional clause that requires equal graph names to be associated with equal graphs.
> 
> Therefore, the quoting semantics is *not minimal*. Quite the opposite. It is not a "weak" semantics at all, because it makes it very easy to derive contradictions, and contradictions are *very strong* semantic effects.
> 
> I also agree with Antoine that formalizing the notion of "no semantics" is pointless.
> 
> My conclusion is that our viable options are: 
> 
> a) to say nothing regarding the semantics of datasets, or
> b) to define a minimal version of a "truth-based"/"entailment-based" semantics (where [[ :i1 { G } ]] entails [[ :i1 { G' } ]] if graph G entails graph G').
> 
> Best,
> Richard


----
Ivan Herman, W3C Semantic Web Activity Lead
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Received on Thursday, 23 August 2012 15:23:59 UTC

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