Re: updated draft

On 04/02/2017 11:47 AM, james anderson wrote:
> good evening;
> 
>> On 2017-04-02, at 20:28, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
>>
>>
>> […]
>>
>> How can this be read other than
>>
>> substitute(BGP(?x :q :b),{(x,_:c)} = BGP(_:c :q :b)
> 
> 
> yes the recommendation definitions are not specific as to whether this happens in the lexical domain or in a model domain.
> one is free to pick.
> you - and so far as i recall, the authors of the paper(s) which led to this “issue”, chose the lexical domain.
> that leads, as is to be expected, to problems.
> in which case, at least one reader of those papers wondered, why this avenue was necessarily selected, when - as is the case with other aspects of sparql interpretation, one is permitted to, and is better off to perform such operations in a model value domain and, in addition, not necessarily statically.
> 
> you do not believe this.
> that is ok.
> i maintain a sparql processor which does, which i understand to conform to the recommendation, but which does not exhibit the problems which you insist must apply.
> that leads me to believe, the deficiency is in the “lexical” interpretation, not in the recommendation.
> 
> best regards, from berlin,
> ---
> james anderson | james@dydra.com | http://dydra.com

That is correct.  I believe that the wording in
https://www.w3.org/TR/sparql11-query/ admits only one reading for this.

In SPARQL substitute happens on expressions in the SPARQL algebra, replacing
variables by their bindings, which are RDF terms.  The result of this
substitution is an expression in the SPARQL algebra.   This resultant
expression is then evaluated, again as per the definitions in
https://www.w3.org/TR/sparql11-query/.  The clear wording from there, in
particular from Section 18.3, is that a blank node in a BGP is subject to an
RDF instance mapping.

There is no reading of https://www.w3.org/TR/sparql11-query/ that can result
in anything else, even though the end result is counter-intuitive.


There is then the question of what should happen.  However, that is a
different question from the question of what the definition of SPARQL in
https://www.w3.org/TR/sparql11-query/ says does happen.

peter

Received on Sunday, 2 April 2017 19:05:26 UTC