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Re: [All] Proposal: RDF Graph Identification

From: Sandro Hawke <sandro@w3.org>
Date: Mon, 20 Aug 2012 11:14:13 -0400
Message-ID: <50325445.6080000@w3.org>
To: Pat Hayes <phayes@ihmc.us>
CC: Ivan Herman <ivan@w3.org>, David Wood <david@3roundstones.com>, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>, W3C RDF WG <public-rdf-wg@w3.org>
On 08/18/2012 06:08 PM, Pat Hayes wrote:
> On Aug 17, 2012, at 11:26 PM, Ivan Herman wrote:
>
>> On Aug 17, 2012, at 18:44 , Pat Hayes wrote:
>>
>>> On Aug 17, 2012, at 3:34 AM, Ivan Herman wrote:
>>>
>>>> On Aug 16, 2012, at 23:40 , Pat Hayes wrote:
>>>>
>>>>> On Aug 16, 2012, at 4:00 PM, David Wood wrote:
>>>>>
>>>>>> On Aug 16, 2012, at 14:20, Ivan Herman <ivan@w3.org> wrote:
>>>>>>>> Mutability only requires changes to the semantics if mutability is perceived as having semantic consequences. So a good place to start might be to ask anyone who thinks it does, to come up with an example involving mutability and entailment (or consistency). For example, if we have explicit time snapshots, then an inconsistency which appears when times can be inferred to overlap might be such an example.
>>>>>>>>
>>>>>>>>> Pat has said in the past that perhaps we should forgo a semantics for RDF given the widely divergent interpretations in the wild.  I (and others) don't think we can or should just throw away the semantics, if for no other reason than OWL, RIF, etc, currently depend on them.
>>>>>>>> Well, actually they don't. Both OWL and RIF have their own, normative, sematnics defined independently of RDF.
>>>>>>>>
>>>>>>> I cannot check it right now (I write this mail from my mobile) but as far as I remember the RDF compatible semantics of OWL 2 explicitly refers back to the RDF Semantics (of course the 2004 version) in its definiton. To be checked, though.
>>>>>> OWL 2004 Semantics clearly references both RDF 2004 Concepts and RDF 2004 Semantics normatively [1].
>>>>> Yes, but it also says that the "direct semantics" is normative for OWL and if there is any clash between that and the RDF-compatible semantics, then the direct semantics wins. So OWL can survive even if RDF semantics goes away.
>>>> Hm. The direct semantics (ie, DL):
>>>>
>>>> http://www.w3.org/TR/2009/REC-owl2-direct-semantics-20091027/
>>>>
>>>> makes actually no reference to the RDF semantics at all (or to RDF, for that matter, except for the exchange format being RDF).
>>>>
>>>> On the other hand, the RDF Based semantics:
>>>>
>>>> http://www.w3.org/TR/2009/REC-owl2-rdf-based-semantics-20091027/
>>>>
>>>> says:
>>>>
>>>> [[[
>>>> Technically, the OWL 2 RDF-Based Semantics is defined as a semantic extension of "D-Entailment" (RDFS with datatype support), as specified in the RDF Semantics [RDF Semantics]. In other words, the meaning given to an RDF graph by the OWL 2 RDF-Based Semantics includes the meaning provided by the semantics of RDFS with datatypes, and additional meaning is specified for all the language constructs of OWL 2, such as Boolean connectives, sub property chains and qualified cardinality restrictions (see the OWL 2 Structural Specification [OWL 2 Specification] for further information on all the language constructs of OWL 2). The definition of the semantics for the extra constructs follows the design principles as applied to the RDF Semantics.
>>>>
>>>> The content of this document is not meant to be self-contained but builds on top of the RDF Semantics document [RDF Semantics] by adding those aspects that are specific to OWL 2. Hence, the complete definition of the OWL 2 RDF-Based Semantics is given by the combination of both the RDF Semantics document and the document at hand. In particular, the terminology used in the RDF Semantics is reused here except for cases where a conflict exists with the rest of the OWL 2 specification.
>>>> ]]]
>>>>
>>>> This means that if we invalidated the RDF Semantics document we would pull the rug from under the RDF based semantics of OWL (which is actually the semantics the RDF people *really* care about in OWL, though Peter may kill me for this remark:-).
>>>>
>>>> Let us not go down that route.
>>> I wasnt suggesting "invalidating" the semantics exactly, only making it non-normative. If you want to use RDF under the old semantic rules, that is fine, even recommended. But you can also use it other ways without being considered bad, and you can even, wait for it, completely ignore the semantics and not have to try to read that part of the spec documents. As only a small percentage of RDF users have read it, this seems like a win-win.
>>>
>> Technically, that may be true. But I have to pull, my apologies for that, a formal problem. We would end up having a normative part in one recommendation normatively refer to an informative section of another recommendation. That may raise eyebrows.
> Ah. I had not thought about that point, I confess. Hmm. There has to be a way around this.

There is -- we're not talking about making it "non-normative", we're 
talking about making it optional, in the same sense that the OWL 2 
RDF-Based Semantics (aka OWL Full) is optional.      That spec is 
normative: if you're doing OWL Full, then this spec says what you must do.

We'd just be separating the RDF semantics from the RDF model and 
syntax.   It would now be okay, according to the spec, to use the RDF 
model and syntax without using the RDF semantics.

OWL and RIF, because they chose to use the RDF semantics, would of 
course be bound by them.

    -- Sandro



> Pat
>
>> (Of course, one can argue that OWL2 refers to the 2004 version of RDF, but if we supersede the 2004 version with RDF 1.1 this may not hold either.)
>>
>> Ivan
>>
>>
>>
>>
>>
>>> Pat
>>>
>>>>
>>>>> In fact, the OWL specs could be rewritten much more simply if RDF had no semantics at all.
>>>> "Could be": maybe. But will not be...
>>>>
>>>> Ivan
>>>>
>>>>> I think something similar is true for RIF, but Sandro can speak to that with more authority.
>>>>>
>>>>> Pat
>>>>>
>>>>>> Regards,
>>>>>> Dave
>>>>>>
>>>>>> [1] http://www.w3.org/TR/owl-semantics/#references-normative
>>>>>>
>>>>>>
>>>>>>> Ivan
>>>>>>>
>>>>>>>
>>>>>>>> ------------------------------------------------------------
>>>>>>>> IHMC                                     (850)434 8903 or (650)494 3973
>>>>>>>> 40 South Alcaniz St.           (850)202 4416   office
>>>>>>>> Pensacola                            (850)202 4440   fax
>>>>>>>> FL 32502                              (850)291 0667   mobile
>>>>>>>> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>> ------------------------------------------------------------
>>>>> IHMC                                     (850)434 8903 or (650)494 3973
>>>>> 40 South Alcaniz St.           (850)202 4416   office
>>>>> Pensacola                            (850)202 4440   fax
>>>>> FL 32502                              (850)291 0667   mobile
>>>>> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>> ----
>>>> Ivan Herman, W3C Semantic Web Activity Lead
>>>> Home: http://www.w3.org/People/Ivan/
>>>> mobile: +31-641044153
>>>> FOAF: http://www.ivan-herman.net/foaf.rdf
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>> ------------------------------------------------------------
>>> IHMC                                     (850)434 8903 or (650)494 3973
>>> 40 South Alcaniz St.           (850)202 4416   office
>>> Pensacola                            (850)202 4440   fax
>>> FL 32502                              (850)291 0667   mobile
>>> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>>>
>>>
>>>
>>>
>>>
>>
>> ----
>> Ivan Herman, W3C Semantic Web Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> mobile: +31-641044153
>> FOAF: http://www.ivan-herman.net/foaf.rdf
>>
>>
>>
>>
>>
>>
>>
> ------------------------------------------------------------
> IHMC                                     (850)434 8903 or (650)494 3973
> 40 South Alcaniz St.           (850)202 4416   office
> Pensacola                            (850)202 4440   fax
> FL 32502                              (850)291 0667   mobile
> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>
>
>
>
>
>
>
Received on Monday, 20 August 2012 15:14:28 UTC

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