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Re: Drafting definitions for select expressions

From: Axel Polleres <axel.polleres@deri.org>
Date: Tue, 8 Dec 2009 12:50:51 +0000
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <4C5D2947-9B84-4A71-90B1-A8C168C65482@deri.org>
To: Axel Polleres <axel.polleres@deri.org>, Andy Seaborne <andy.seaborne@talis.com>
p.s.: 
 just two questions which I don't really get yet in the proposal on [1] yet, before I forget...
 
1) Does this mapping cover left-to-right evaluation as in [2], is it intended to?
2) I understand that the case discusseed in [3] is forbidden by this definition, yes?

Hear you in two hours...

thanks,
Axel

1. http://www.w3.org/2009/sparql/docs/query-1.1/select-expr-defs-1-1.html
2. http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0418.html
3. http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0425.html

On 8 Dec 2009, at 12:29, Axel Polleres wrote:

> when I looked into this...
> 
> 1)
> ... I suppose:
> 
> extend(μ, var, expr) = { (var,value) | var not in dom(μ) and value = eval(expr) }
> extend(μ, var, expr) = μ if var not in dom(μ) and eval(expr) is an error
> extend is undefined when var in dom(μ).
> 
>    
> should be:
> 
> 
> extend(&mu;, var, expr) =
> (i)   { (var,value) | value = eval(expr) } &cup; &mu; ... if var not in dom(&mu;) and eval(expr) is defined
> (ii)  &mu; ... if var not in dom(&mu;) and eval(expr) is an error
> (iii) undefined ... if var in dom(&mu;).
> 
> 2) I am somewhat hesitant about forbidding
> 
>  _:blank AS ?Var
> 
>  if we don't have sub-CONSTRUCTs, since if I can't "mint" new bnodes I think I can't model
>  one of the use cases I had in mind fir sub CONSTRUCTs.
>  (related to ACTION-133)
> 
> best,
> Axel
> 
> On 25 Nov 2009, at 14:08, Andy Seaborne wrote:
> 
> > Here is an early draft of definitions for select expressions covering
> > algebra, evaluation, and translation from syntax to algebra.
> >
> > This is a temporary working document prior to integration into the main
> > document.
> >
> > Comments and fixes welcome: please note it is very much a
> > work-in-progress draft
> >
> > http://www.w3.org/2009/sparql/docs/query-1.1/select-expr-defs-1-1.html
> >
> >         Andy
> >
> >
> 
> 
> 
Received on Tuesday, 8 December 2009 12:51:36 GMT

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