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Re: [RDF-CONCEPTS] Skolemization

From: David Booth <david@dbooth.org>
Date: Wed, 12 Jun 2013 11:53:44 -0400
Message-ID: <51B89988.9040903@dbooth.org>
To: Ivan Herman <ivan@w3.org>
CC: public-rdf-comments <public-rdf-comments@w3.org>
On 06/12/2013 10:04 AM, Ivan Herman 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
>>
>>
>> Regarding: "Systems wishing to do this SHOULD mint a new, globally unique IRI (a
>> Skolem IRI) for each blank node so replaced." it seems to me that this
>> conformance requirement should be a MUST -- not a SHOULD -- because the system
>> has already made the free choice to skolemize.
>
> I do not follow this. Why should be a MUST?

Because an IRI that is not globally unique would not be logically 
equivalent to a bnode, and thus could significantly change the 
semantics, and that would violate the intent of skolemization.  If it 
were a SHOULD then

   _:b :foo :bar .

could be changed to

   :bar :foo :bar .

If someone makes a change like that they should not be able to claim 
that the change was conformant to the RDF spec.

Bear in mind that the decision to perform the skolemization is still 
optional -- it's a MAY.  The MUST only kicks in after they have made 
that choice: if they choose to do it they MUST do it properly.

David

>
> Ivan
>
>
>>
>> Specific wording changes that I suggest:
>>
>> 1. Change:
>>
>>      "Systems wishing to do this SHOULD mint a new, globally
>>      unique IRI (a Skolem IRI) for each blank node so replaced."
>>
>> to:
>>
>>      "Systems choosing to do this MUST mint a new, globally
>>      unique IRI (a Skolem IRI) for each blank node so replaced.
>>      Each such Skolem IRI SHOULD conform to the syntactic
>>      requirement for a well-known IRI [WELL-KNOWN] with the
>>      registered name genid. This is an IRI that uses the HTTP or
>>      HTTPS scheme, or another scheme that has been specified to
>>      use well-known IRIs; and whose path component starts with
>>      /.well-known/genid/."
>>
>> 2. Delete the paragraph:
>> [[
>> Systems that want Skolem IRIs to be recognizable outside of the system
>> boundaries should use a well-known IRI [WELL-KNOWN] with the registered name
>> genid. This is an IRI that uses the HTTP or HTTPS scheme, or another scheme that
>> has been specified to use well-known IRIs; and whose path component starts with
>> /.well-known/genid/.
>> ]]
>>
>> Thanks,
>> David
>>
>
Received on Wednesday, 12 June 2013 15:54:12 UTC

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