[jira] [Commented] (JENA-780) Single use extend expressions could be substituted directly for their later usage

["Rob Vesse (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JENA-780?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14126790#comment-14126790 ] 

Rob Vesse commented on JENA-780:
--------------------------------

Retitled this issue because I think this is a more general rewrite.  Any extend expression whose value is used only once in a place where an expression could be used instead can have the extend eliminating and the expression substituted directly at the relevant point.

So this would cover {{BIND}}'s whose values is used only once in a {{FILTER}}, another {{BIND}}, an {{ORDER BY}}, a {{GROUP BY}} or a {{HAVING}}

> Single use extend expressions could be substituted directly for their later usage
> ---------------------------------------------------------------------------------
>
>                 Key: JENA-780
>                 URL: https://issues.apache.org/jira/browse/JENA-780
>             Project: Apache Jena
>          Issue Type: Improvement
>          Components: ARQ, Optimizer
>    Affects Versions: Jena 2.12.0
>            Reporter: Rob Vesse
>            Priority: Minor
>
> This RFE is a follow on from JENA-779, the query with a sub-optimal plan there uses a {{BIND}} to create a value which is then only used once in a subsequent filter.
> Actually that query uses it twice but I think the general approach I am trying to describe in this RFE bears consideration.  In this case it seems like it would be possible to substitute the extend expression for the bound variable in the filter expression.
> Simplified variant of original query such that the bound value is only used once:
> {noformat}
> SELECT DISTINCT ?uri
> {
>   { ?uri ?p ?o }
>   UNION
>   {
>     ?sub ?p ?uri
>     FILTER(isIRI(?uri))
>   }
>   BIND(str(?uri) as ?s)
>   FILTER(STRSTARTS(?s, "http://"))
> }
> {noformat}
> Rewritten query:
> {noformat}
> SELECT DISTINCT ?domainName
> {
>   { ?uri ?p ?o }
>   UNION
>   {
>     ?sub ?p ?uri
>     FILTER(isIRI(?uri))
>   }
>   FILTER(STRSTARTS(str(?uri), "http://"))
> }
> {noformat}
> Which avoids an extend expression whose value is only used once and will ultimately be thrown away.
> From a {{Transform}} standpoint this is likely awkward to implement in a pure transform since it requires knowledge about the query structure above the {{FILTER}} i.e. whether the bound variable is used elsewhere and so would need to use before and after visitors to track that additional state but I think this is a feasible optimisation.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)