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Re: DELETE and blank nodes

From: Ivan Herman <ivan@w3.org>
Date: Wed, 03 Mar 2010 13:26:04 +0100
Message-ID: <4B8E555C.6040004@w3.org>
To: Lee Feigenbaum <lee@thefigtrees.net>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
Hi Lee,

first of all, thanks a lot for this write up. It was very helpful (at
least to me).

On 2010-3-3 07:16 , Lee Feigenbaum wrote:
[snip the explanation to save space]
> 
> == The Proposals ==
> 
> I see only two realistic proposals emerging from this.
> 
> 1/ We prohibit blank nodes in the DELETE template completely.
> 
> 2/ Blank nodes in DELETE templates act as "wild cards"--effectively
> variables pre-bound to all RDF terms--to let us write some shortcuts and
> handle Sandro's case of deleting RDF lists. We prohibit the same blank
> node label from being used in multiple scopes.
> 
> 
> 
> == My Opinion ==
> 
> While I'm sympathetic to Sandro's use case, I'm frightened of the fact
> that:
> 
>   DELETE { _:b1 :p :o } WHERE { }
> and
>   DELETE { ?b1 :p :o } WHERE { }
> 
> do dramatically different things. Because of this, I'd rather we go with
> the first proposal and prohibit blank nodes in the DELETE template
> entirely.

I think Sandro's use case is important. Eg, this is the only way we can
manipulate, via SPARQL UPDATE, RDF graphs encoding OWL constructs or, if
Sandro's RIF-in-RDF encoding is done, RIF rules. With entailment regimes
around the corner, I think this is important. (And yes, as you say, the
restriction on non-named blank nodes is difficult to justify.)

I actually do not find your example so confusing. The only point where
people might be confused, probably, is that

DELETE {_:a :b :c }

is disallowed. But that can be explained.

Ie, I would prefer to go with solution (2) as described above.

> 
> hope this is helpful,

As I said, very. Thanks!

Ivan

> Lee
> 
> 
> 
> 
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
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Received on Wednesday, 3 March 2010 12:26:02 GMT

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