Re: [Owlim-discussion] strange behaviour of BigOWLIM answering empty query

[Ivan Peikov]

Peter,

After a brief discussion of the issue you reported we found out that the 
SPARQL's specification has a special treatment of the empty group pattern:

---qte--------------------------------------------------------------------------
5.2.1 Empty Group Pattern

The group pattern:

{ }
matches any graph (including the empty graph) with one solution that does not 
bind any variables. For example:

SELECT ?x
WHERE {}
matches with one solution in which variable x is not bound.
---eqt--------------------------------------------------------------------------

So in this very case OWLIM correctly follows the spec and this is not a bug.

I also find this behavior strange. I believe it originated by SPARQL authors' 
desire to handle group patterns like:

  {
    ?x foaf:name ?name .
    {}
    ?x foaf:mbox ?mbox .
  }

In such occasions the {} should not affect the whole group (it should be 
ignored). If it did return 0 matches the whole group being an intersection of 
the pattern resultsets would return 0 matches.

Anyway..


Cheers,
Ivan


On Monday 17 May 2010 15:18:17 Ivan Peikov wrote:
> Hi Peter,
>
> This is indeed a bug. We'll file and address it as soon as possible.
> Thanks for reporting!
>
>
> Cheers,
> Ivan
>
> On Monday 17 May 2010 14:58:18 Peter Kostelnik, PhD. wrote:
> > hi there ..
> >
> > we've hitted the strange behaviour of BigOWLIM answering the empty query
> > .. in our case, the query is generated automatically and for this case:
> >
> > SELECT ?anything WHERE {}
> >
> > the one empty result is returned .. and ?anything is bound to the empty
> > string ..
> >
> > did we find the bug or we are missing something?
> >
> > thanks in advance, cheers,
> >                       Peter K.
> >
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> > OWLIM-discussion@ontotext.com
> > http://ontotext.com/mailman/listinfo/owlim-discussion
>
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