On 19/07/12 01:52, Simon Helsen wrote:
Sorry, I am looking at this again. Are you saying that in
(prefix ((p1: <file:///C:/Temp/t1>)
(p2: <file:///C:/Temp/t2>))
(distinct
(project (?R1 ?optionalValue)
(conditional
(assign ((?R1 <https://perfrrs.ibm.com:9443/rm/resources/_r1>))
(bgp (triple <https://perfrrs.ibm.com:9443/rm/resources/_r1>
p1:pr1 <https://perfjts.ibm.com:9443/jts/process/project-areas/p>)))
(bgp (triple ?R1 p2:pr2 ?optionalValue))))))
?R1 is not always bound to
<https://perfrrs.ibm.com:9443/rm/resources/_r1>?
It is bound - (conditional) flows the bindings from the left into the
right. It's a left-index-join with no scope restrictions.
(conditional) and (sequence) are used when there are no scope issues
arise (e.g. doubly nested optionals with no use of the var in the
middele optiona, use of FILTER variables in out-of-scope places)
And therefore, are you
saying that ?R1 can be any value which satisfies p2:pr2 ?optionalValue ?
I still don't understand why the assign optimization cannot be pushed
into the optional in the query
I don't know why the optimization is taking place. I would have
expected it to occur in the shorter example at least and the longer one
looks like the same structure (when you indent the thing - the
sparql.org query validator pretty prints queries - its a web service
around the engine of arq.qparse). But I haven't looked at the code
in-depth yet to see if some corner case is blocking it or whether it is
something to do with a change in the order optimization strategies are
applied.
Andy
PREFIX p1:<t1>
PREFIX p2:<t2>
SELECT DISTINCT ?R1 ?optionalValue
WHERE
{
?R1 p1:pr1 <https://perfjts.ibm.com:9443/jts/process/project-areas/p>
OPTIONAL
{ ?R1 p2:pr2 ?optionalValue }
FILTER ( ?R1 = <https://perfrrs.ibm.com:9443/rm/resources/_r1>)
}
is there perhaps a different way to express this?
Simon
From: Andy Seaborne <[email protected]>
To: Simon Helsen/Toronto/IBM@IBMCA
Cc: [email protected]
Date: 07/18/2012 05:42 PM
Subject: Re: optimization opportunity lost in 2.7.x which existed in
2.6.x?
------------------------------------------------------------------------
On 18/07/12 16:25, Simon Helsen wrote:
> Andy,
>
> I have simplified the scenario a little bit. So the following query
>
> PREFIX p1:<t1>
> PREFIX p2:<t2>
> SELECT DISTINCT ?R1 ?optionalValue
> WHERE
> {
> ?R1 p1:pr1 <https://host:9443/jts/process/project-areas/p>
> FILTER ( ?R1 = <https://host:9443/rm/resources/_r1>)
> OPTIONAL
> { ?R1 p2:pr2 ?optionalValue }
> }
>
> leads to
>
> (prefix ((p1: <file:///C:/Temp/t1>)
> (p2: <file:///C:/Temp/t2>))
> (distinct
> (project (?R1 ?optionalValue)
> (filter (= ?R1 <https://host:9443/rm/resources/_r1>)
> (conditional
> (bgp (triple ?R1 p1:pr1
> <https://host:9443/jts/process/project-areas/p>))
> (bgp (triple ?R1 p2:pr2 ?optionalValue)))))))
>
> whereas the following query
>
> PREFIX p1:<t1>
> PREFIX p2:<t2>
> SELECT DISTINCT ?R1 ?optionalValue
> WHERE
> {
> {
> ?R1 p1:pr1 <https://host:9443/jts/process/project-areas/p>
> FILTER ( ?R1 = <https://host:9443/rm/resources/_r1>)
> }
> OPTIONAL
> { ?R1 p2:pr2 ?optionalValue }
> }
>
> leads to
>
> (prefix ((p1: <file:///C:/Temp/t1>)
> (p2: <file:///C:/Temp/t2>))
> (distinct
> (project (?R1 ?optionalValue)
> (conditional
> (assign ((?R1 <https://host:9443/rm/resources/_r1>))
> (bgp (triple <https:/host:9443/rm/resources/_r1> p1:pr1
> <https://perfjts.ibm.com:9443/jts/process/project-areas/p>)))
> (bgp (triple ?R1 p2:pr2 ?optionalValue))))))
>
> So, looking at this in more detail, the former plan surprises me a bit
> because it proposes to evaluate p1:pr1 as optional, even though I didn't
> express that in the query.
Yes, you did.
"conditional" is a binary operator, an optimized for of leftjoin. The
first arg is the fixed side and the second args the conditional part.
{ ?s ?p ?o OPTIONAL { ?s1 ?p1 ?o1 } }
becomes
(leftjoin
(bgp (triple ?s ?p ?o)
(bgp (triple ?s1 ?p1 ?o1))
which is executed as
(conditional
(bgp (triple ?s ?p ?o)
(bgp (triple ?s1 ?p1 ?o1))
(sequence) is rather different.
> WHERE
> {
> {
> ?R1 p1:pr1 <https://host:9443/jts/process/project-areas/p>
> FILTER ( ?R1 = <https://host:9443/rm/resources/_r1>)
> }
> OPTIONAL
> { ?R1 p2:pr2 ?optionalValue }
> }
is a different query because FILTERS are group-wide, a group being what
is between {} (caveat a special case in OPTIONAL not occuring here).
Adding the extra {} means the FILTER is applied to
?R1 p1:pr1 <https://host:9443/jts/process/project-areas/p>
alone.
Andy
