[[ Rushed answer - more later ]]
The function that needs to change is :
com.hp.hpl.jena.sparql.path.eval
PathEngine.doOne
specifically the call to Graph.find.
If that consulted the property function registry
(also check other .find calls in that package - there are very few).
Test cases (JUnit code ideally) would be good; patches are better.
Andy
PS and any speed ups would also be good. The code can be become
expensive if it's in an intense part of the query.
On 29/01/14 14:07, Joshua TAYLOR wrote:
On Wed, Jan 29, 2014 at 12:32 AM, Rob Vesse <[email protected]> wrote:
Most likely no, did you try printing the algebra for the query?
This would show you whether the query plan contains a propertyfunc
operator or not.
Thanks, I haven't worked with these kind of extensions before, so I
didn't really know where to start. Here are the algebra expressions
for simplified queries. The property function is called in the first
case (with (triple _ p _)), but not in the second (with (path* p)).
Neither algebra contains a propertyfunc operator, though. Do I need
to expand this farther or something?
Query: select * { ?s <java:CBDSPARQLExample$sameBlank> ?o }
Algebra: (bgp (triple ?s <java:CBDSPARQLExample$sameBlank> ?o))
Query: select * { ?s <java:CBDSPARQLExample$sameBlank>* ?o }
Algebra: (path ?s (path* <java:CBDSPARQLExample$sameBlank>) ?o)
Through some more experimentation, the property function isn't called
for (seq … p …), either. I think this is problematic. For the `*`
case, things might be complicated, but consider a sequence pattern.
According to 9.2 Examples [1] from the SPARQL 1.1 recommendation,
[[[
Sequence: Find the names of people 2 "foaf:knows" links away.
{
?x foaf:mbox <mailto:alice@example> .
?x foaf:knows/foaf:knows/foaf:name ?name .
}
This is the same as the SPARQL query:
SELECT ?x ?name
{
?x foaf:mbox <mailto:alice@example> .
?x foaf:knows [ foaf:knows [ foaf:name ?name ]].
}
]]]
Of course, the SPARQL recommendation doesn't address Jena's property
functions, but with the current behavior, property functions will be
called in:
Query: select * { ?s <java:CBDSPARQLExample$sameBlank> [
<java:CBDSPARQLExample$sameBlank> ?o ] }
Algebra: (bgp
(triple ?s <java:CBDSPARQLExample$sameBlank> ??0)
(triple ??0 <java:CBDSPARQLExample$sameBlank> ?o)
)
but not in:
Query: select * { ?s
<java:CBDSPARQLExample$sameBlank>/<java:CBDSPARQLExample$sameBlank> ?o
}
Algebra: (path ?s (seq <java:CBDSPARQLExample$sameBlank>
<java:CBDSPARQLExample$sameBlank>) ?o)
I did run those queries on some data, and observed the log output
indicating that the property function is run in the first case, but
not the second. I think this is counterintuitive behavior, since what
the SPARQL rec says is equivalent has different behavior. I haven't
looked into how property paths are matched, so I don't know how hard
this is to adjust.
If this seems like something that isn't intended behavior (or even
just isn't documented), I'd be happy to make a minimal example
demonstrating the issue and put it on JIRA.
//JT
[1] http://www.w3.org/TR/sparql11-query/#propertypath-examples
