Hi,
I am trying to understand how NamedGraphs work in Jena+TDB and how to use
SPARQL for the purpose. The API that I found as an eventual candidate that
would fit the task is GraphStore. My initial understanding was that GraphStore
is a kind of facade on top of the TDB store that should be used in a case of
incoming UPDATE query if there is a chance that the query eventually deals with
NamedGraphs. However, the test gives somewhat unexpected results (suggesting
that the GraphStore may actually be deep copy of the store?).
What am I missing here? I am afraid that my understanding of the conceptual
model of NamedGraphs in Jena+TDB is not correct. How should the SPARQL query
processing be organized in the case of TDB store working with named graphs?
Regards,
Milorad
public class rdfStoreNamedGraphsTesting {
/**
* @param args
*/
public static void main(String[] args) {
File m_baseDir;
Model m_triplestore;
Dataset m_dataset;
String baseDirPath = "C:\\Temp";
m_baseDir = new File(baseDirPath+File.separator+"tdb");
boolean succ = m_baseDir.exists() && m_baseDir.isDirectory();
if(!succ) succ = m_baseDir.mkdir();
if(!succ){
m_baseDir = null;
m_triplestore = null;
m_dataset = null;
System.err.print("Error opening/creating new folder: "+baseDirPath);
}else{
m_dataset = TDBFactory.createDataset(m_baseDir.getPath()) ;
m_triplestore = m_dataset.getDefaultModel();
}
String querystr;
/**
* Select distinct NamedGraphs in the store
*/
querystr = "SELECT DISTINCT ?g WHERE { GRAPH ?g { } }";
System.out.println("Running "+querystr);
Query query = QueryFactory.create(querystr);
query.setPrefixMapping(m_triplestore);
m_triplestore.enterCriticalSection(Lock.READ) ;
try {
QueryExecution qexec = QueryExecutionFactory.create(query,
m_triplestore) ;
ResultSet results = qexec.execSelect() ;
System.out.println("============= Query result ============");
ResultSetFormatter.output(System.out, results,
ResultSetFormat.syntaxText);
System.out.println("============= Query result ============");
GraphStore graphStore = GraphStoreFactory.create(m_triplestore) ;
System.out.println("GRAPHS number in store is "+graphStore.size());
qexec.close();
} finally {
m_triplestore.leaveCriticalSection();
}
/**
* Create new NamedGraph in the store
*/
querystr = "CREATE GRAPH <http://example.com/graphs/test1/>";
System.out.println("Running "+querystr);
m_triplestore.enterCriticalSection(Lock.WRITE) ;
try {
UpdateRequest updateRequest = UpdateFactory.create(querystr);
updateRequest.setPrefixMapping(m_triplestore);
GraphStore graphStore = GraphStoreFactory.create(m_triplestore) ;
UpdateAction.execute(updateRequest, graphStore);
System.out.println("GRAPHS number in GraphStore is
"+graphStore.size());
}catch (Exception e){
System.err.println(e);
} finally {
m_triplestore.commit();
m_triplestore.getLock().leaveCriticalSection();
TDB.sync(m_triplestore);
}
/**
* Select distinct NamedGraphs in the store
*/
querystr = "SELECT DISTINCT ?g WHERE { GRAPH ?g { } }";
System.out.println("Running "+querystr);
query = QueryFactory.create(querystr);
query.setPrefixMapping(m_triplestore);
m_triplestore.enterCriticalSection(Lock.READ) ;
try {
QueryExecution qexec = QueryExecutionFactory.create(query,
m_triplestore) ;
ResultSet results = qexec.execSelect() ;
System.out.println("============= Query result ============");
ResultSetFormatter.output(System.out, results,
ResultSetFormat.syntaxText);
System.out.println("============= Query result ============");
GraphStore graphStore = GraphStoreFactory.create(m_triplestore) ;
System.out.println("GRAPHS number in store is "+graphStore.size());
qexec.close();
} finally {
m_triplestore.leaveCriticalSection();
}
System.out.println("==== finished ====");
m_triplestore.close();
}
}
