Re: DELETE and blank nodes

Birte,

although we agree on our choice on the original issue at hand, I have a
clarification question... Is your mental model such that once the
variable binding is done, based on the WHERE clause, the semantics of
DELETE is that all triples are deleted that can be inferred by the
DELETE template's triples?

This is not defined and section 9 of the entailment document leaves that
option open. That being said I agree (if this is indeed what you have in
mind) that we should not make this approach impossible via syntactic
means...

Ivan



On 2010-3-3 18:04 , Birte Glimm wrote:
> On 3 March 2010 15:40, Andy Seaborne <andy.seaborne@talis.com> wrote:
>>
>>
>> On 03/03/2010 3:32 PM, Birte Glimm wrote:
>>>
>>> Thanks a lot Lee for the great summary!
>>>
>>> On 3 March 2010 06:16, Lee Feigenbaum<lee@thefigtrees.net>  wrote:
>>>
>>> [snip]
>>>
>>>>>  == The Proposals ==
>>>>>
>>>>>  I see only two realistic proposals emerging from this.
>>>>>
>>>>>  1/ We prohibit blank nodes in the DELETE template completely.
>>>
>>> This might work nicely for simple entailment, but will not work for
>>> OWL (maybe RIF too). E.g., if I have a statement that Peter has some
>>> parent who's a Lawyer, I can say that in OWL functional-style syntax
>>> with:
>>> ClassAssertion(ObjectSomeValuesFrom(ex:hasParent ex:Lawyer) ex:Peter)
>>> For this, the (normative) mapping to triples gives:
>>> ex:Peter a _:x.
>>> _:x a owl:restriction .
>>> _:x owl:onProperty ex:hasParent .
>>> _:x owl:someValuesFrom ex:Person .
>>
>> ex:Lawyer?
> 
> Ups, yes.
> 
>>> for a fresh bnode _:x. There is no way to represent this OWL statement
>>> without bnodes, but it is always possible to use a square bracker
>>> form.
>>
>> I think Lee is referring to syntactic use of bnodes in a delete template,
>> not bnodes that might be found by a query pattern and bound to a variable.
>> So _:x is a new bnode not the bnode with that label in the data.
>>
>> It would be deleted by:
>>
>> DELETE WHERE
>> {
>>  ex:Peter a ?var.
>>  ?var a owl:restriction .
>>  ?var owl:onProperty ex:hasParent .
>>  ?var owl:someValuesFrom ex:Lawyer .
>> }
>>
>> using variables with ?var binding to exactly the bnode that was syntactical
>> _:x in the data.
> 
> Unfortunately not, because such a bnode binding will be filtered out
> from the results by the conditions on answers. If it were not filtered
> out, you could get infinite results because replacing _:x with :_xx or
> _:xxx or ... would equally be entailed. Since we use entailment, using
> the same sub-graph criterion that simple entailment uses to limit
> answers with just different bnode labels does not really work for
> entailments. For anonymous individuals in OWL (bnodes in individual
> positions) we use skolemisation, but the bnodes that are just used to
> represent some concepts are invisible to the reasoner and skolemising
> them is quite strange for Direct Semantics. Such a BGP would, actually
> not even be legal under Direct Semantics because it cannot really be
> turned into an OWL structural object.
> 
> Birte
> 
> 
>>        Andy
>>
>>
> 
> 
> 

-- 

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