Rob Vesse created JENA-780:
------------------------------
Summary: Extend expression whose value is used only in a filter
can be substituted directly into the filter
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. In this case it seems like it would be possible to substitute the
extend expression for the bound variable in the filter expression.
Original query:
{noformat}
SELECT DISTINCT ?domainName
{
{ ?uri ?p ?o }
UNION
{
?sub ?p ?uri
FILTER(isIRI(?uri))
}
BIND(str(?uri) as ?s)
FILTER(STRSTARTS(?s, "http://";))
BIND(IRI(CONCAT("http://";, STRBEFORE(SUBSTR(?s,8), "/"))) AS ?domainName)
}
{noformat}
Rewritten query:
{noformat}
SELECT DISTINCT ?domainName
{
{ ?uri ?p ?o }
UNION
{
?sub ?p ?uri
FILTER(isIRI(?uri))
}
FILTER(STRSTARTS(str(?uri), "http://";))
BIND(IRI(CONCAT("http://";, STRBEFORE(SUBSTR(?s,8), "/"))) AS ?domainName)
}
{noformat}
Which avoids one extend expression whose value 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}} and so would need to use before and after visitors to track that
>additional state but I think this is a feasible optimisation.
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