Sparql substract instance - sparql

Question

I have an anthology, I created an interface for evaluation or there is a submit button. This button allows you to calculate the difference between the old value and the value 20. I try to select an instance with sparql and I would evaluate an instance subtracts the old value with the value 20.
valider.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
Model m=ModelFactory.createMemModelMaker().createModel(null);
FileManager.get().readModel( m, owlFile );
String myOntologyName = "ProjetHela";
String uri="file:///C:/Project/Krs1.owl";
// Définition de prefixe pour simplifier l'utilisation de SPARQL
String reuses = "maj: <"+RDF.getURI()+">" ;
// String myOntologyPrefix = "PREFIX "+myOntologyName+": <"+myOntologyNS+">" ;
String myOntologyPrefix = "PREFIX "+myOntologyName+": <"+uri+">" ;
// if (liste.getSelectedItem().toString().equals("GMP: Puissance=60352 Watt,limite supérieure= 73500 Watt")) {
String queryString=
"PREFIX maj: <http://www.owl-ontologies.com/reuses.owl#>"
+ "SELECT ?hasnameevaluated"
+ " WHERE "
+ "{"
+ "?Besoin maj:hasnameevaluated ?hasnameevaluated "
+"FILTER (?hasnameevaluated - 20) "
+ " } ";
Query query = QueryFactory.create(queryString) ;
QueryExecution qexec = QueryExecutionFactory.create(query, m) ;
try {
ResultSet rs = qexec.execSelect() ;
// Affichage des resultats
for ( ; rs.hasNext() ; ){
//System.out.print("");
QuerySolution rb = rs.nextSolution() ;
String y = rb.getLiteral("hasnameevaluated").getString();
System.out.println( " " + y);
}} finally {
qexec.close() ;
}
}
}
);
but it doesn't work
please help me

Answer 1

FILTER (?hasnameevaluated - 20)
is a test , not an assignment of a value.
Did you mean to use:
BIND (?hasnameevaluated - 20 AS ?newvalue)
or
SELECT ?hasnameevaluated (?hasnameevaluated - 20 AS ?newvalue) WHERE