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Posted to users@jena.apache.org by Joshua TAYLOR <jo...@gmail.com> on 2013/10/15 14:21:23 UTC
Can a blank node be used as the object of a (transitive) property path?
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/resource/>
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/%3C4F4019B6.1030006@apache.org%3E
--
Joshua Taylor, http://www.cs.rpi.edu/~tayloj/
Re: Can a blank node be used as the object of a (transitive) property
path?
Posted by Dave Reynolds <da...@gmail.com>.
On 15/10/13 13:21, Joshua TAYLOR wrote:
[snip]
> I've looked through the SPARQL 1.1 grammar, and traced down through
>
> GroupGraphPattern
> GroupGraphPatternSub
> TriplesBlock
> TriplesSameSubjectPath
> PropertyListPathNotEmpty
> ObjectListPath
> ObjectPath
> GraphNodePath
> VarOrTerm
Doesn't GraphNodePath have two branches:
GraphNodePath ::= VarOrTerm | TriplesNodePath
which takes you down:
TriplesNodePath
BlankNodePropertyListPath
to
'[' PropertyListPathNotEmpty ']'
Dave
Re: Can a blank node be used as the object of a (transitive) property path?
Posted by Joshua TAYLOR <jo...@gmail.com>.
Thanks both, Dave and Andy. This is exactly what I needed. It just
seemed similar enough to the grammar bug that we ran into earlier that
I wanted to check here first. Off to virtuoso-users I go with this
information…
Thanks, especially for the quick turnaround!
//JT
On Tue, Oct 15, 2013 at 8:52 AM, Andy Seaborne <an...@apache.org> wrote:
> 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/%3C4F4019B6.1030006@apache.org%3E
>>
>
--
Joshua Taylor, http://www.cs.rpi.edu/~tayloj/
Re: Can a blank node be used as the object of a (transitive) property
path?
Posted by Andy Seaborne <an...@apache.org>.
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/%3C4F4019B6.1030006@apache.org%3E
>
Re: Can a blank node be used as the object of a (transitive) property
path?
Posted by Rob Vesse <rv...@dotnetrdf.org>.
This is perfectly legal and Jena is correct in allowing it.
GraphNodePath can go down the TriplesNodePath route:
[105] GraphNodePath ::= VarOrTerm | TriplesNodePath
TriplesNodePath can go down the BlankNodePropertyListPath route:
[100] TriplesNodePath ::= CollectionPath | BlankNodePropertyListPath
And BlankNodePropertyListPath allows exactly the style of syntax you've
written:
[101] BlankNodePropertyListPath ::= '[' PropertyListPathNodeEmpty ']'
So the bug is with Virtuoso
Hope this helps,
Rob
On 15/10/2013 13:21, "Joshua TAYLOR" <jo...@gmail.com> 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/resource/>
> 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/%3C4F4019B
>6.1030006@apache.org%3E
>--
>Joshua Taylor, http://www.cs.rpi.edu/~tayloj/