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Re: [RDF-CONCEPTS] Skolemization

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 15 Jun 2013 22:25:59 -0500
Cc: Ivan Herman <ivan@w3.org>, public-rdf-comments <public-rdf-comments@w3.org>
Message-Id: <1CB1ED6A-B87B-4313-8277-5C55C359F164@ihmc.us>
To: David Booth <david@dbooth.org>

On Jun 15, 2013, at 9:38 PM, David Booth wrote:

> On 06/15/2013 10:01 PM, Pat Hayes wrote:
> 
>>>>>>>>>>>> David Booth wrote:
>>>>>>>>>>>>> I'd like to propose a small change in section
>>>>>>>>>>>>> on Skolemization:
>>>>>>>>>>>>> https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#section-skolemization
> [ . . . ]
>> I do not understand in what sense RFC2119 language can be applied to
>> a definition. What behavior would we be prohibiting?
> 
> it isn't about behavior.  it is about conformance to a definition.
> the RDF specification defines what constitutes RDF, and uses conformance terms as in the following sentence:  "IRIs in the RDF abstract syntax MUST be absolute, and MAY contain a fragment identifier."  Those conformance terms must be normative to have effect.

Right, and that text does have an influence on software behavior. For example, it licences applications to reject RDF which contains IRIs that do not conform. What analogous prohibition or requirement would be the consequence of putting a MUST in the definition of skolemization? RDF engines can skolemize RDF and they can also do many other things to RDF. If they do something that does not fit the definition of skolemizing, then they have done something which is not skolemizing. By definition. But adding a MUST to the definition changes nothing about what they are required to do or prohibited from doing. 

> 
> similarly the definition of RDF skolemization needs to be normative, with conformance terms, for the exact same reason.
> 
> if someone transformed
> 
>  _:b :foo :bar .
> 
> into
> 
>  :bar :foo :bar .
> 
> then they should be prohibited from calling it RDF skolemization, just as people are currently prohibited from calling the following RDF:
> 
>  "literal" _:bnode  "oops" .

Its not about calling things names. They can *call* that RDF all they like, but a conforming RDF engine will spit it out, is the point. But there isn't anything about skolemization that engines are required to do or prohibited from doing. They can do it, or not; and they can do other things, or not. If someone says their engine is doing skolemization when it isn't, then they are wrong, which can be checked by looking at the definitions. But just because their own tray tables are not in the fully upright and locked position does not make their RDF engine nonconformant. 

Pat


> 
> David
> 
> 
> 

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Received on Sunday, 16 June 2013 03:26:24 UTC

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