XML 1.1 for sparql-results is incompatible with Jena clients

[jimkont]

The following commit introduced problems with Jena clients (probably due to a xerces library bug).
b7bf790

The problems were reported by users of http://dbpedia.org but it will affect all VOS instanced updated to latest develop branch

An example using Jena that shows the problem is

sparql --data empty.ttl "SELECT * { SERVICE <http://dbpedia.org/sparql> { ?s ?p ?o } } LIMIT 1"

and produces this stack trace

Failed when initializing the StAX parsing engine
com.hp.hpl.jena.sparql.resultset.ResultSetException: Failed when initializing the StAX parsing engine
    at com.hp.hpl.jena.sparql.resultset.XMLInputStAX.<init>(XMLInputStAX.java:110)
    at com.hp.hpl.jena.sparql.resultset.XMLInput.make(XMLInput.java:81)
    at com.hp.hpl.jena.sparql.resultset.XMLInput.fromXML(XMLInput.java:39)
    at com.hp.hpl.jena.sparql.resultset.XMLInput.fromXML(XMLInput.java:34)
    at com.hp.hpl.jena.query.ResultSetFactory.fromXML(ResultSetFactory.java:309)
    at com.hp.hpl.jena.sparql.engine.http.Service.exec(Service.java:191)
    at com.hp.hpl.jena.sparql.engine.main.iterator.QueryIterService.nextStage(QueryIterService.java:56)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIterRepeatApply.makeNextStage(QueryIterRepeatApply.java:110)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIterRepeatApply.hasNextBinding(QueryIterRepeatApply.java:67)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIterSlice.hasNextBinding(QueryIterSlice.java:76)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:40)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:40)
    at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
    at com.hp.hpl.jena.sparql.engine.ResultSetStream.hasNext(ResultSetStream.java:75)
    at com.hp.hpl.jena.sparql.engine.ResultSetCheckCondition.hasNext(ResultSetCheckCondition.java:59)
    at com.hp.hpl.jena.sparql.resultset.ResultSetMem.<init>(ResultSetMem.java:97)
    at com.hp.hpl.jena.query.ResultSetFactory.makeRewindable(ResultSetFactory.java:419)
    at com.hp.hpl.jena.sparql.resultset.TextOutput.write(TextOutput.java:149)
    at com.hp.hpl.jena.sparql.resultset.TextOutput.write(TextOutput.java:132)
    at com.hp.hpl.jena.sparql.resultset.TextOutput.write(TextOutput.java:120)
    at com.hp.hpl.jena.sparql.resultset.TextOutput.format(TextOutput.java:65)
    at com.hp.hpl.jena.query.ResultSetFormatter.out(ResultSetFormatter.java:166)
    at com.hp.hpl.jena.sparql.util.QueryExecUtils.outputResultSet(QueryExecUtils.java:160)
    at com.hp.hpl.jena.sparql.util.QueryExecUtils.doSelectQuery(QueryExecUtils.java:199)
    at com.hp.hpl.jena.sparql.util.QueryExecUtils.executeQuery(QueryExecUtils.java:80)
    at arq.query.queryExec(query.java:208)
    at arq.query.exec(query.java:159)
    at arq.cmdline.CmdMain.mainMethod(CmdMain.java:102)
    at arq.cmdline.CmdMain.mainRun(CmdMain.java:63)
    at arq.cmdline.CmdMain.mainRun(CmdMain.java:50)
    at arq.sparql.main(sparql.java:28)
Caused by: java.lang.NullPointerException
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl.scanStartElement(XML11NSDocumentScannerImpl.java:356)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2786)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606)
    at com.sun.org.apache.xerces.internal.impl.XML11NSDocumentScannerImpl.next(XML11NSDocumentScannerImpl.java:857)
    at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:558)
    at com.hp.hpl.jena.sparql.resultset.XMLInputStAX$ResultSetStAX.processHead(XMLInputStAX.java:379)
    at com.hp.hpl.jena.sparql.resultset.XMLInputStAX$ResultSetStAX.init(XMLInputStAX.java:195)
    at com.hp.hpl.jena.sparql.resultset.XMLInputStAX$ResultSetStAX.<init>(XMLInputStAX.java:187)
    at com.hp.hpl.jena.sparql.resultset.XMLInputStAX.worker(XMLInputStAX.java:147)
    at com.hp.hpl.jena.sparql.resultset.XMLInputStAX.<init>(XMLInputStAX.java:106)
    ... 33 more

[HughWilliams]

@jimkont: So, Jena (or its parser engine) does not support results in XML 1.1 format ?

Is there a simple test case for recreating this behaviour ?

[jimkont]

This is probably a bug in the xml parsing library Jena that is using (Xerces).
If you install Jena locally from https://jena.apache.org/documentation/tools/
and run the following commands you will get the error stack trace described above:

touch empty.ttl # just an empty turtle
sparql --data empty.ttl "SELECT * { SERVICE <http://dbpedia.org/sparql> { ?s ?p ?o } } LIMIT 1"

Unless this is important, I suggest you revert this commit back until a fix is made in Jena.
Jena is a very common client so this will probably bring many complaints in the future

[HughWilliams]

@jimkont: OK, i have been able to recreate and reported to development to look into ...

[HughWilliams]

@jimkont: The commit has been reverted:

http://sourceforge.net/p/virtuoso/virtuoso-opensource/ci/f1cf34ad3dec2bf1db53a29c311d1b2a2662b994

The dbpedia binary will soon be updated with this update ...

[jimkont]

Noticed that already! Thanks a lot @HughWilliams

[pfps]

So I, who have been waiting for this fix since last September, have to wait longer because of other buggy software? Surely the right way to do this was to get the Xerxes software fixed.

[dwvisser]

Has anybody filed a bug report with the Xerces project? (Or alternatively, could someone share the appropriate issue tracker here?)

[pfps]

On further examination, it appears that it may not be a current Xerces bug.

A comment in b7bf790 indicates that the problem is with "the standard OpenJDK XML parser" which is apparently based on Xerces 2.7.

There are workarounds given at https://issues.apache.org/jira/browse/JENA-942.

So, what should be done? Something is pulling in an old buggy XML parser. This appears to be either Jena or OpenJDK.

I'm finding it astonishing that progress is being blocked today because there is still software that does not correctly handle XML 1.1, which came out in 2006. I think that the best way forward is to produce a method for not using the offending software and then tell people who are using it to use the new method Software that can't handle XML 1.1 should be put in the ash can.