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Re: agenda for tomorrow...

From: Axel Polleres <axel.polleres@deri.org>
Date: Mon, 7 Dec 2009 21:21:16 +0000
Cc: "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-Id: <43E6C844-54E1-44B3-9319-DB8FC21FECC8@deri.org>
To: Andy Seaborne <andy.seaborne@talis.com>
Thanks, appreciated. I put a link to the strawman proposal for variable scope to the agenda.

Axel


On 7 Dec 2009, at 18:53, Andy Seaborne wrote:

> 
> 
> On 07/12/2009 17:57, Axel Polleres wrote:
> > ... will be sent out later tonite:
> 
> Sorry for this very rushed email but I am unable to spend time on
> SPARQL-WG tomorrow morning and anyway that would be too late for many
> people to have had a chance to catch up.
> 
> > Essentially, I plan to discuss the issues not covered last time
> > * Do aggregate functions need to be set off syntactically?
> 
> Steve sends his regrets:
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0571.html
> 
> > * Scope of alias variables
> 
> ISSUE-39
> 
> Nearby: ISSUE-41, ISSUE-12
> 
> Rather than a general discussion, can we start with a strawman:
> 
> Discussion emails:
> 
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0411.html
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0414.html
> 
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0418.html
> 
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0423.html
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009OctDec/0425.html
>    (NB typo in that message)
> 
> Strawman:
> 
> Expressions do not have side-effects.
> 
> Legal:
> # ?C can be used in a expression to the right,
> # but not left, of it's definition.
> SELECT (count(*) AS ?C)  (?Num/?C AS ?X)
> 
> Legal:
> # 2009OctDec/0414.html
> # HAVING, and ORDER BY, can reference a project variable.
> select ?x count(?doc) as ?count where {
> ?x :hasCreated ?doc
> }
> group by ?x
> having (?count > 10)
> 
> This one crosses aggregates and select expressions so is not in [1] and
> complicates Step 2 and Step 3 of modifier translation but they are
> already needing reworking anyway so that aggregates can be used in HAVING:
> 
>   having (count(?doc) > 10)
> 
> In outline, the translation is:
> 
> SELECT covers two operators: extend and project. Put the "extend"
> operations as in [1] immediate around the group (just after the algebra
> for GROUP BY and aggregate calculation and just before HAVING) and the
> projection outside the HAVING.  They are already in this order in [1] -
> it's just extending it to HAVING.
> 
> pattern => group inc aggregate calculation =>
>     extends => having => order by => project =>
>       distinct => reduced => offset/limit
> 
> With the SELECT expressions currently, it's no possible to introduce a
> variable then project it away.
> 
> Illegal:
> # Can't use a variable introduced  in a SELECT expression inside the
> SELECTs pattern.
> 
> SELECT (?x+1 AS ?y)  { ... ?y ... }
> is illegal scoping (see [1]) and is a static syntax check.
> 
>         Andy
> 
> > plus (time allowed)
> > * Andy's proposal for SELECT expressions [1]
> 
> ACTION-134
> 
> I propose
> 
> SELECT ( _:b1 AS ?blank )
> 
> is not legal in the grammar, that is blank nodes can not be used in
> expressions for select-expressions (which is good ebcause they are not
> legal in expressions in FILTER currently.
> 
>         Andy
> 
> >
> > details to follow, apologies
> >
> > Axel
> >
> >
> > 1. http://www.w3.org/2009/sparql/docs/query-1.1/select-expr-defs-1-1.html
> 
> [2]
> http://www.w3.org/2005/10/Process-20051014/policies.html#GeneralMeetings
> 
Received on Monday, 7 December 2009 21:21:51 GMT

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