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Re: Views on the outcomes of F2F

From: Steve Harris <steve.harris@garlik.com>
Date: Thu, 12 Nov 2009 16:01:10 +0000
Cc: Lee Feigenbaum <lee@thefigtrees.net>, SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <E4E22204-20D4-4E7C-AAE7-FB23C452CA03@garlik.com>
To: Andy Seaborne <andy.seaborne@talis.com>
On 11 Nov 2009, at 09:34, Andy Seaborne wrote:
> On 10/11/2009 21:45, Lee Feigenbaum wrote:
>> Andy Seaborne wrote:
>>>
>>> On 10/11/2009 20:18, Steve Harris wrote:
>>> > We're explicitly not chartered to do assignment - if that makes  
>>> sense -
>>> > somewhat tortured English. We voted on a list of things to be in  
>>> the
>>> > charter, and assignment was on the list that didn't make it.
>>>> You could regard it as syntactic sugar for subselect + project
>>>> expressions, but that doesn't appear to be what Holger is after,  
>>>> and
>>>> it's a little sophisitic to argue that IMHO.
>>>
>>> We have now have had feedback that the assumption that SELECT
>>> expression syntax is not sufficient. We can respond to comments.
>>>
>>> I believe Holger is asking for nothing more than syntactic sugar.
>>> Jeremy's syntactic conversion from LET to SELECT expressions shows
>>> what they want and it's a syntactic rewrite even SPARQL syntax to
>>> SPARQL syntax.
>>
>> I couldn't follow the transformation. Can you explain it, please? I'm
>> trying to figure out if it matches what is implemented in Open Anzo  
>> or not.
>
> If that would help the WG; I'll write a separate email.  The  
> clarification should come from the commenter, rather than my  
> interpretation, but I'm sure we can ask them to comment on the  
> description.
>
> It would also be helpful if you describe what OpenAnzo does. (ditto  
> other impls).  I hope that Steve will provide the concrete example  
> of what he thinks Holger is asking for and any examples that concern  
> him.

So, my reading of Holger's request is that he would like [my examples,  
not his]

data:
<s> <p> <o> .

SELECT *
WHERE {
   LET(?x := ?y)
   OPTIONAL { <s> <p> ?y }
}

?x = unbound, ?y = <o>

SELECT *
WHERE {
   OPTIONAL { <s> <p> ?y }
   LET(?x := ?y)
}

?y = <o>, ?x = <o>

i.e. a true assignment as BASIC programmers would understand it.  
However, based on what Lee has said I think I just got the wrong end  
of the stick.

I got the impression that Jeremy was in favour of a macro-substitution- 
like operator, based on what he said at the F2F. He provided a  
definition by email, but I wasn't able to follow it, so again, the  
wrong end of the stick is a definite possibility.

- Steve

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Received on Thursday, 12 November 2009 16:01:48 GMT

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