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Re: Drafting definitions for select expressions

From: Axel Polleres <axel.polleres@deri.org>
Date: Tue, 8 Dec 2009 12:29:16 +0000
Cc: "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-Id: <DD87C744-90B7-4BD9-8DA6-3764ABA96D17@deri.org>
To: Andy Seaborne <andy.seaborne@talis.com>
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 12:29:56 GMT

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