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Re: ISSUE-68: Simpler definition of pre-binding

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Thu, 28 Apr 2016 07:45:47 -0700
To: Holger Knublauch <holger@topquadrant.com>, public-data-shapes-wg@w3.org
Message-ID: <5722221B.6060202@gmail.com>
>From 18.2.3 of SPARQL 1.1 Query Language, Examples of Mapped Graph Patterns

Example: Pattern involving BIND:

{ ?s :p ?v . BIND (2*?v AS ?v2) ?s :p1 ?v2 }

Join(
   Extend( BGP(?s :p ?v), ?v2, 2*?v) ,
   BGP(?s :p1 ?v2) )

Note that ?v2 is unchanged even though it is bound at the point of the second
basic graph pattern.

Basic graph patterns are processed by matching, not evaluation.  Matching of
basic graph patterns does not involve evaluating the variables in them.  See
18.3.1 for more details.

peter




On 04/21/2016 10:04 PM, Holger Knublauch wrote:
> On 21/04/2016 22:20, Peter F. Patel-Schneider wrote:
>> Sure, basic graph patterns are processed in SPARQL, but this process (Section
>> 18.3) does not involve evaluation of variables in basic graph patterns.  An
>> implementation of the current spec would not be licensed to do replacement in
>> basic graph patterns.
> 
> I disagree that BGPs do not evaluate variables (they take prior bindings, e.g.
> from nested elements, into account). Also my definition does not talk about
> replacement in BGPs, but only about injecting additional values into the
> stream of bindings that is used whenever an element is evaluated.
> 
> I have no idea how to proceed here, as this dialog between myself and Peter
> seems to run in circles. Is there anyone else here in the WG who has problems
> with my current definition, e.g. implementers would not know what to do?
> 
> Holger
> 
>>
>> This may be only a matter of terminology.  However the spec is currently so
>> imprecise that in many places it is not possible for me to determine the
>> intent of the spec.
>>
>> When I encounter places where the intent of the spec is undeterminable or the
>> spec is imprecise or self-contradictory I point them out.  It is vital that
>> all these places are fixed before the working group is finished.  It is best
>> to fix these places as soon as possible as it is quite often the case that
>> elucidating the places where intent is unclear or there are imprecisions or
>> contradictions will bring out significant problems.
> 
> 
Received on Thursday, 28 April 2016 14:46:20 UTC

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