Re: SPARQL EXISTS variations

Hi EXISTS TF members,

I have updated my document after last Friday's discussion.

https://gist.github.com/hartig/3fffc7a02f3e0411158298e313b4c9c2


Most importantly, I have added a detailed discussion of all cases
possible for the pattern within an EXISTS expression---see the section
called "Why is a similar change not needed for the other cases?"

I have also tried to add the document into the repo [1], but somehow
the CI run of the corresponding PR failed. Until this is fixed, the
link above is the most recent version of the document.

-Olaf

[1] https://github.com/w3c/sparql-query/pull/270



On Fri, 2025-08-22 at 11:03 +0000, Olaf Hartig wrote:
> Hi,
>
> As the different variations were mentioned only informally in Peter's
> email, I wanted to convince myself that we can
> also define them formally in the spec. For the DEEP INJECTION
> variations it was not immediately clear to me how this
> could be done; especially not for the OVERALL-variant of DEEP
> INJECTION.
>
> I found a way to do it (based on an idea that Andy mentioned during
> the last TF meeting), and wrote a short document to
> describe the exact changes that are needed:
>
> https://gist.github.com/hartig/3fffc7a02f3e0411158298e313b4c9c2

>
>
> Best,
> Olaf
>
>
> On Thu, 2025-08-21 at 10:09 +0000, Olaf Hartig wrote:
> > On Thu, 2025-08-21 at 03:17 +0200, James Anderson wrote:
> > > On 20. Aug 2025, at 22:30, Andy Seaborne <andy@apache.org> wrote:
> > > > On 16/08/2025 15:45, Peter F. Patel-Schneider wrote:
> > > > > There was again discussion in the SPARQL EXISTS task force on
> > > > > different solutions to the SPARQL EXISTS
> > > > > problems.
> > > > > The solutions amount to, roughly:
> > > > > Simple LEFTJOIN, where no bindings from outside the EXISTS
> > > > > affect the pattern inside.
> > > >
> > > > SEMIJOIN?
> > >
> > > is it not the case that, where no variable from the solution is
> > > free in the exists pattern, that pattern reduces to
> > > a
> > > boolean constant value which depends only on the state of the
> > > target graph?
> >
> > What do you mean with a variable being "free in the exists
> > pattern"?
> >
> > I agree with Andy, it is a SEMIJOIN.
> >
> > @Peter, thanks for this great summary! I agree with your believe
> > that ONCE versus OVERALL is relevant only for DEEP
> > INJECTION.
> >
> > -Olaf
> >
> >
> > > >
> > > > > Values injection at the beginning of the pattern (SHALLOW
> > > > > INJECTION).
> > > > > Values injection inside the pattern (DEEP INJECTION), with
> > > > > two variations
> > > > > values projected out in sub-SELECTs are not affected
> > > > > (PROJECTION) and
> > > > > values projected out in sub-SELECTs are affected.
> > > >
> > > >
> > > >
> > >
> > > ---
> > > james anderson | james@dydra.com |
> > > https://dydra.com/

> > >
> > >
> > >
> >
>

Received on Sunday, 24 August 2025 18:54:54 UTC