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Re: [RDF-CONCEPTS] Skolemization

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Wed, 12 Jun 2013 23:43:49 -0700
Message-ID: <51B96A25.7090006@gmail.com>
To: David Booth <david@dbooth.org>
CC: Ivan Herman <ivan@w3.org>, public-rdf-comments <public-rdf-comments@w3.org>
How can any system be entirely sure that any IRI it mints for skolemization 
*is* globally unique?  If this is not possible, and I fail to see how it can 
be possible, then no system could ever do skolemization under the *must* wording.

peter

On 06/12/2013 08:53 AM, David Booth wrote:
> 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 Thursday, 13 June 2013 06:44:18 UTC

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