On 10/15/13 9:05 AM, 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/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 asked about it on the Jena-users list (since the validator is Jena-based), and got this response from Andy Seaborne: """ 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 ObjectPathObjectPath ::= 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. """ Is this a bug in Virtuoso, or something that's a product of some configuration, or DBpedia using an older version, or… ? 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/%3c4f4019b6.1030...@apache.org%3E
Here's the query expressed differently: 1. http://kingsley.idehen.net/c/DBMKAE -- query results 2. http://kingsley.idehen.net/c/DBNJEL -- query definition. -- Regards, Kingsley Idehen Founder & CEO OpenLink Software Company Web: http://www.openlinksw.com Personal Weblog: http://www.openlinksw.com/blog/~kidehen Twitter/Identi.ca handle: @kidehen Google+ Profile: https://plus.google.com/112399767740508618350/about LinkedIn Profile: http://www.linkedin.com/in/kidehen
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