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Re: [RDF-CONCEPTS] Skolemization

From: Ivan Herman <ivan@w3.org>
Date: Mon, 17 Jun 2013 08:54:03 +0200
Message-ID: <51BEB28B.90003@w3.org>
To: David Booth <david@dbooth.org>
CC: Niklas Lindström <lindstream@gmail.com>, Pat Hayes <phayes@ihmc.us>, public-rdf-comments <public-rdf-comments@w3.org>

David Booth wrote:
> On 06/16/2013 06:22 AM, Ivan Herman wrote:
>> I have not looked at the text right now (I am on a mobile), and that may be good
>> at this moment, because it shows what I remember the intention was...
>> I guess the question of David could/should be boiled down to: is the
>> Skolemization part normative or not? I think we never meant that to be normative
>> in the group; if it says so in the document, that is a mistake (Pat already
>> alluded to that). If it is non normative, then the usage of an RFC MUST would
>> become fairly meaningless... Is there any reason we would make it normative?
>> This request never came up in the group before; the whole skolemization was
>> presented as a good practice to follow if one wants to get rid of bnodes when
>> exchanging graphs.
>> (Systems may skolemize for any other reason, eg, for internal purposes or
>> exchanging data with other instantiation of the same software only, and they may
>> decide to use some sort of a UUID based URI which would be just as fine. If we
>> set a 'must' for the genid way, then a UUID based skolemization might be
>> considered as illegal:-(
> aha!  I think I see where the confusion lies, and I apologize for not noticing
> this sooner.  :(
> I believe we are talking about two different kinds of skolemization. the first
> is what I will call *unconstrained* skolemization, and this is the process of
> properly substituting arbitrary new IRIs for bnodes.  for this, any kind of IRI 
> will do.  the second I will call *round-trippable* skolemization, and this
> *requires* that the IRIs be minted using the "genid" well-known suffix, so that
> they can be Predictably recognized by other parties.
> the definition of *unconstrained* skolemization does not need to be normative,
> because other parties will not be depending on recognizing its result.  but the
> definition of *round-trippable* skolemization *does* need to be normative, so
> that other parties acting independently can Predictably recognize the
> *round-trippable* skolem IRIs and turn them back into bnodes if desired.

Well... even that can be questioned, just to play it hard ball:-).
Round-trippable skolemization without prior agreement is where the current
skolem approach is handy. I mean, if you and I exchange data and we agree to use
a particular skolem scheme, than we achieve what we want...

I am a little bit afraid we get into too much details here. If the intention of
skolemizing is to broadcast the data to the wide world for round tripping, then
the skolemization in the document is the obvious answer, and anybody in their
sane mind would go for that. I am not sure this would require the additional
step of making it normative with a MUST (but that is the WG to decide, I am
fairly neutral about it)


> does that make more sense now?
> David

Ivan Herman, W3C
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153

Received on Monday, 17 June 2013 06:54:33 UTC

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