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Re: [sub-select] Some examples and discussion

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Fri, 13 Mar 2009 20:53:22 -0400
To: "Lee Feigenbaum" <lee@thefigtrees.net>
cc: "Seaborne, Andy" <andy.seaborne@hp.com>, "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-ID: <C5E07842.8567%ogbujic@ccf.org>
Originally, I was concerned that arbitrarily-nested sub-selects might
introduce some non-linear recursion that using ASK as FILTER expressions
does not.  So, the limitations I had in mind were syntactic and ensured the
recursion in sub-selects are not of the more complex kind.

However, the scoping effect of group graph patterns used with sub-selects
seems to ensure that computations within a sub-select are local to the group
graph pattern with the exception of the solutions returned:

SELECT ...
{
   { SELECT ...
     {
       ...
     }
   }
}

I'm not so sure about whether the proposed assignment syntax provides the
same (or similar) guarantees.

-- Chimezie

On 3/12/09 9:21 PM, "Lee Feigenbaum" <lee@thefigtrees.net> wrote:

> Chimezie Ogbuji wrote:
>> On 3/12/09 9:14 AM, "Seaborne, Andy" <andy.seaborne@hp.com> wrote:
>>> As for implementation, putting subs-selects was not hard when I added the
>>> functionality in ARQ and I didn't have an existing DB engine to pull
>>> existing
>>> features from.  I don't think it was luck that other designs decisions had
>>> set
>>> things up, more it was a natural step.  Other opinions may differ.
>>> What is hard, as had been pointed out, is optimization, but that is not to
>>> be
>>> specified.
>> 
>> I don't think I agree that optimization and implementation effort (which is
>> a direct consequence of the complexity introduced by more expressive query
>> forms such as sub-selects) should *not* be a factor.  In fact, it is mostly
>> my concern in this regard that motivates me to suggest that we consider a
>> spectrum of sub-select features to include.
> 
> Chime, I was intrigued by your suggestion regarding a limited form of
> sub-select on the teleconference, but admit that I couldn't immediately
> see what that would look like. Do you have a concrete proposal for how
> this might work? (just a sketch would be helpful!)
> 
> thanks,
> Lee
> 


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Received on Saturday, 14 March 2009 00:54:19 GMT

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