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Re: Fix to the rq25 spec for BIND

From: Steve Harris <steve.harris@garlik.com>
Date: Fri, 24 Aug 2012 14:00:36 +0100
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <DC337E8C-302F-4429-977D-402A109F75D5@garlik.com>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
OK, but what was the strange behaviour of the LC1-2 design which caused us to change it in the first place?

Sorry if I missed some discussion, but I imagine it wasn't done on a whim…

- Steve

On 24 Aug 2012, at 11:47, Andy Seaborne wrote:

> This completes ACTION-673.
> 
> The design has been reverted to that of 1LC and 2LC
> 
> 1/ Informative text changed.
> 2/ Variable Scope section has a paragraph specifically on BIND
> 3/ Algebra translation translation reverts to previous text (and special on BIND removed)
> 
> No execution tests are invalidated.
> 
> Reverting the scope rules affects syntax tests:
>    syntax-BINDscope7.rq
>    syntax-BINDscope8.rq
> which are now bad syntax.
> 
> 
> A few notes about the BIND fix:
> 
> This is illegal under both designs:
> 
> SELECT *
> {
>   ?s ?p ?o
>   BIND("foo" AS ?o)
> }
> 
> This is illegal on the reverted design:
> 
> SELECT * {
>    ?s ?p ?o
>    OPTIONAL{?s ?p2 ?o2}
>    BIND(5 AS ?o2)
> }
> 
> 
> And note adding {} (which are not a subquery with project) does not make any difference:
> 
> SELECT *
> {
>   { ?s ?p ?o }
>   BIND("foo" AS ?o)	# Bad
> }
> 
> because it is still a previous element of a group so the accumulated scope of that element shows up in the group BIND is in - i.e. it includes all of { ?s ?p ?o }
> 
> which makes sense because we want BIND to apply a previous element like:
> 
> SELECT * {
>   { ?s ?p ?o } UNION {?s ?p2 ?o2}
>   BIND(5 AS ?o)       # Bad
>  }
> 
> 
> Legal: masked
> 
> SELECT *
> {
>   { SELECT ?s { ?s ?p ?o } }
>   BIND("foo" AS ?o)	# GOOD
> }
> 
> Legal: scope rules do not extend outwards of {} in which BIND is used.
> 
> SELECT *
> {
>   { ?s ?p ?o }
>   UNION
>   { BIND("foo" AS ?o) }	# GOOD
> }
> 

-- 
Steve Harris, CTO
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Received on Friday, 24 August 2012 13:01:13 GMT

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