Re: Fix to the rq25 spec for BIND

On 24/08/12 14:00, Steve Harris wrote:
> OK, but what was the strange behaviour of the LC1-2 design which caused us to change it in the first place?

Unclarity esp. of the informal text.  The 3LC was an attempt to minimise 
change - I messed it up by not properly considering the scope of the 
expression and it didn't work.

	Andy

>
> 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
>> }
>>
>

Received on Friday, 24 August 2012 13:57:03 UTC