[JENA-199] BindingBase can hit a null pointer exception on certain queries against a TDB dataset

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Not A Problem
• Component/s: TDB
• Labels: csv results sparql tdb tsv
• Assignee: Unassigned
• Reporter: Rob Vesse
• Created: 19/Jan/12 22:11
• Updated: 02/Feb/12 17:19
• Resolved: 02/Feb/12 17:19

Description

This is a strange bug which I have been unable to reduce to a more minimal example than the files I will attach so I apologize for that.

Essentially the problem manifests as follows, when using a TDB dataset with Fuseki some queries will return blank output if the user requests Text, CSV or TSV. When using XML/JSON the output is fine.

The test data used is SP2B 10k, two of the SP2B queries that exhibit this issue are as follows:

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX bench: <http://localhost/vocabulary/bench/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>

SELECT DISTINCT ?person ?name
WHERE {
?article rdf:type bench:Article .
?article dc:creator ?person .
?inproc rdf:type bench:Inproceedings .
?inproc dc:creator ?person .
?person foaf:name ?name
}

And:

PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>

SELECT DISTINCT ?name
WHERE {
?erdoes rdf:type foaf:Person .
?erdoes foaf:name "Paul Erdoes"^^xsd:string .

{ ?document dc:creator ?erdoes . ?document dc:creator ?author . ?document2 dc:creator ?author . ?document2 dc:creator ?author2 . ?author2 foaf:name ?name FILTER (?author!=?erdoes && ?document2!=?document && ?author2!=?erdoes && ?author2!=?author) }

UNION

{ ?document dc:creator ?erdoes. ?document dc:creator ?author. ?author foaf:name ?name FILTER (?author!=?erdoes) }

}

I will attach these as files as well for convenience.

If you run Fuseki with a memory dataset using the --mem option, load this data and run the same queries the Text, CSV and TSV output works fine. This implies that there is something in the TDB code related to its return of results or iterators which somehow causes the Text, CSV and TSV formatters to either error or to believe that they have no results to format.

I'm completely unfamiliar with the TDB codebase so I haven't attempted to discover what the cause of the issue is though I may poke around anyway