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Re: ISSUE-30: How does SPARQL's notion of RDF dataset relate our notion of multiple graphs?

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 16 Apr 2011 18:10:42 -0500
Cc: Ivan Herman <ivan@w3.org>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <9B010BD8-2175-4B46-94C2-E1765FC0357B@ihmc.us>
To: Richard Cyganiak <richard@cyganiak.de>

On Apr 16, 2011, at 5:53 PM, Richard Cyganiak wrote:

> Pat,
> 
> On 16 Apr 2011, at 22:50, Pat Hayes wrote:
>>> This part of SPARQL is successful and useful despite being disconnected from the RDF Model Theory. RDF Datasets as they are defined in SPARQL have no impact on entailments, and therefore do not require a relation to the RDF Model Theory.
>> 
>> The model theory is the semantics of RDF.
> 
> Yes, that's what it says on top of the document.

I wonder, however, given the rest of your message, if you fully grasp what this means.

> 
>> It bears on any operation on RDF that is sensitive to the meanings of URIs or triples or literals. It is not purely concerned with entailments.
> 
> What operations, beside inference, are you talking about?
> 
> My understanding is that the RDF Model Theory exists to define which inferences are valid, given an RDF graph. What other purpose does it serve?

It defines what RDF means. Or to be achingly precise, it puts constraints upon what RDF can possibly mean. To give just two examples, it implies that the truth of an RDF triple cannot depend upon the form of a URI (other than by this form changing what the URI denotes) and it specifies that any URI must be interpreted as referring to the same entity every place it occurs. These constraints on meaning apply to any RDF processing, not just to entailment checking. SPARQL for example satisfies semantic conditions which are related to the RDF semantics. 

>>> “RDF content” is the triples in the data model.
>> 
>> No, RDF content is the semantic content of the triples in the data model.
> 
> We'll have to agree to disagree here.

Well, I used the phrase, and this is what I meant by it. And I insist that this - the semantics of the triples - is not something that can be ignored while conforming to the RDF specs. Of course, the specs can be ignored, and no doubt often are. But our job is to write the specs., so we are rather obliged to take them seriously.

>> The RDF model theory is normative. It is not something that can be handily ignored just because someone does not like it. 
> 
> *Reality* is normative. It is not something that can be handily ignored just because someone doesn't like it. The RDF model theory, on the other hand, *is* being ignored by most if not all recent successful RDF-based technologies. This does not appear to be to their detriment.

Well, if that is your view, then by all means let us as a WG declare that RDF has no normative model theory, and is simply a meaningless notation. I will be happy to go along with this, which might surprise you. But we should not give our notation a normatively defined semantics and ALSO say that this semantics should be ignored in practice. At the very least, we should present the appearance of intellectual honesty. 

I suggest, in all seriousness, that you put this forward as a WG issue: propose that RDF be declared to have no normative semantics at all. At the very least, the resulting debate might get some issues out into the open air. 

Pat

> 
> Best,
> Richard

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Received on Saturday, 16 April 2011 23:11:14 GMT

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