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Re: reducing/reframing role of RDF Semantics; was Re: [All] Proposal: RDF Graph Identification

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 17 Aug 2012 20:47:18 -0500
Cc: David Wood <david@3roundstones.com>, Ivan Herman <ivan@w3.org>, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>, W3C RDF WG <public-rdf-wg@w3.org>
Message-Id: <AB8099FD-32CA-4573-9AAF-E950ADF53CD4@ihmc.us>
To: Sandro Hawke <sandro@w3.org>

On Aug 17, 2012, at 2:30 PM, Sandro Hawke wrote:

> 
> On 08/16/2012 05:40 PM, 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. In fact, the OWL specs could be rewritten much more simply if RDF had no semantics at all.  I think something similar is true for RIF, but Sandro can speak to that with more authority.
> 
> [not without doing some research that seems unnecessary right now]
> 
> I'm not sure I understand what you're suggesting.   Let me approach it as a strawman proposal which I might support (not sure yet) for reframing how we talk about the RDF Semantics, perhaps getting them more in line with how they are being really used.

OK, but I was meaning something really quite simple: making the RDF semantics non-normative. Then it becomes legal to use RDF any way you want, including your time-snapshots idea, etc.. And of course OWL can (and indeed does) say that it, at least , IS assuming that RDF is bieng used according to it semantics, which is fine, but not actually required any more. 

> Basically, the idea is we reduce the role of what has been called "RDF Semantics" to being another entirely optional "entailment regime" [1], like the various OWL and RIF profiles.  

You could put it that way, except that in order to even have a notion of entailment regime - in fact, to even have the notikon of entailment - you need a model theory first. So this doesnt get rid of the sematnics or change its status. 

>   Instead of saying this is the meaning of the language, we say this is something people might do with RDF graphs.

And that is already true, of course. What I am suggesting is that we say that it is fine to do something else with them (maybe, if you make clear in some way  what it is you are intending to do.) 

> 
> Perhaps the revised document would be titled, "RDF Entailment and Consistency", or "RDF Reasoning", or "RDF Logical Operations", possibly with the word "Core" in there somewhere.

Um. I dont see any reason to change the document title. 
> 
> So, implementers could see it as defining a set of operations

No, no. Semantics is still semantics, not a set of operations. Just an optional semantics, is all. 

> (entailment checking, consistency checking) which they might want to do with RDF Graphs.  Hopefully people not interested in these operations would still be encouraged to do things in such a way that others can sensibly use them with the same data.    But it would be social and market pressures getting people to respect this stuff (as it always really is), without a retreat to "because W3C said so".

Yes to that last point, indeed. 

> So -- in a sense, this is not change at all.  But it is a different framing.     It's no longer "defining the semantics of the language", instead it's defining several entailment regimes to be used with the data structure known as RDF triples.
> 
> Thinking about this for all of 20 minutes, it sounds sensible to me.

OK. I have another idea to try out on you at this point, but lets leave that until later. 

Pat

> 
>    -- Sandro
> 
> [1] http://www.w3.org/TR/sparql11-entailment/
> 
> 
> 
> 

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Received on Saturday, 18 August 2012 01:47:52 UTC

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