Joshua,
It's legal syntax.
[[
Virtuoso 37000 Error SP031: SPARQL compiler: Object of transitive
triple pattern should be variable or QName or literal, not blank node
]]
suggests to me it is not an error in parsing but in
translation/compilation afterwards; it's quite specific to the form
you've used. It might be doing something special for "property*".
> ObjectListPath
> ObjectPath
ObjectPath ::= VarOrTerm | TriplesNodePath
VarOrTerm covers the [] case, not the [ ... ] case.
TriplesNodePath ::= CollectionPath | BlankNodePropertyListPath
BlankNodePropertyListPath ::= '[' PropertyListPathNotEmpty ']'
PropertyListPathNotEmpty ::= ... VerbSimple ObjectListPath ...
matches "?p ?c"
so [ ?prop ?c ] is OK.
Andy
PS The SPARQL validator at sparql.org is the grammar in the spec. The
parser and the HTML comes from the same javacc definition (HTML with a
perl script to format the output of javacc doc). It should be the
post-REC version. ARQ extensions are handled in the same grammar (as
#ifdef !!) so there is no manual intervention between master javacc and
either spec or for the strict SPARQL 1.1 parser. Well, that's the
theory anyway. You'll have to trust me as to the implementation of the
theory.
On 15/10/13 13:21, Joshua TAYLOR wrote:
Hi all,
I recently posted an answer to a Stack Overflow question [1] that led
me to write the query
select ?prop ?c
where {
dbpedia:Milano dbpedia-owl:wikiPageRedirects* [ ?prop ?c ] .
}
and submit it to the DBpedia public endpoint [2] (which has the
appropriate namespace prefixes defined), but I get this error message:
"""
Virtuoso 37000 Error SP031: SPARQL compiler: Object of transitive
triple pattern should be variable or QName or literal, not blank node
SPARQL query:
define sql:big-data-const 0
#output-format:text/html
define sql:signal-void-variables 1 define input:default-graph-uri
<http://dbpedia.org> select ?prop ?c
where {
dbpedia:Milano dbpedia-owl:wikiPageRedirects* [ ?prop ?c ] .
}
"""
If I explicitly define the prefixes
prefix dbpedia: <http://dbpedia.org/resource/>
prefix dbpedia-owl: <http://dbpedia.org/ontology/>
select ?prop ?c
where {
rdf:Milano rdf:wikiPageRedirects* [ ?prop ?c ] .
}
and bring it over to sparql.org's validator, I get no complaints, and
it says the query is equivalent to
1 PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>
2 PREFIX dbpedia: <http://dbpedia.org/resouVirtuoso 37000 Error SP031:
SPARQL compiler: Object of transitive
triple pattern should be variable or QName or literal, not blank node
rce/>
3
4 SELECT ?prop ?c
5 WHERE
6 { dbpedia:Milano (dbpedia-owl:wikiPageRedirects)* _:b0 .
7 _:b0 ?prop ?c
8 }
which makes sense, based on 4.1.4 Syntax for Blank Nodes [4] from the
spec which says:
"""
The following two forms
[ :p "v" ] .
[] :p "v" .
allocate a unique blank node label (here "b57") and are equivalent to writing:
_:b57 :p "v" .
"""
I've looked through the SPARQL 1.1 grammar, and traced down through
GroupGraphPattern
GroupGraphPatternSub
TriplesBlock
TriplesSameSubjectPath
PropertyListPathNotEmpty
ObjectListPath
ObjectPath
GraphNodePath
VarOrTerm
GraphTerm [3]
at which point
[109] GraphTerm ::= iri | RDFLiteral | NumericLiteral |
BooleanLiteral | BlankNode | NIL
[138] BlankNode ::= BLANK_NODE_LABEL | ANON
so it seems like it's not legal (unfortunately).
At first I'd though this might be a Virtuoso bug, since this would be
pretty useful behavior to have, but now it looks like it might be a
bug in the (Jena-based) validator.
This seems like it might be related to an earlier "bug" in the spec
that prevents property paths _within_ blank nodes [5]. Is this a bug
in Jena or in Virtuoso? I'll file the bug report appropriately; I
just need to know where to send it.
Thanks,
//JT
[1] http://stackoverflow.com/q/19380175/1281433
[2] http://dbpedia.org/sparql
[3] http://www.w3.org/TR/sparql11-query/#rGraphTerm
[4] http://www.w3.org/TR/sparql11-query/#QSynBlankNodes
[5]
http://mail-archives.apache.org/mod_mbox/jena-users/201202.mbox/%[email protected]%3E
