Java and SPARQL
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This document discusses processing SPARQL queries using Java with ARQ. It demonstrates how to execute a SPARQL query on an ontology model, print the results, and analyze various aspects of the query such as retrieving result variables, analyzing query elements like triple patterns, and examining the prefix mappings and expressions. The document provides an overview of executing SPARQL queries programmatically using the ARQ processor for Jena.
Java and SPARQL
- 1. Processing SPARQL Queries using Java ARQ - A SPARQL Processor for Jena Raji GHAWI 26/01/2009
- 4. Query Execution Read a file into a model String fileName = "../univ.owl"; // Model model = ModelFactory.createDefaultModel(); OntModel model = ModelFactory.createOntologyModel(OntModelSpec.OWL_DL_MEM); try { File file = new File(fileName); FileReader reader = new FileReader(file); model.read(reader,null); } catch (Exception e) { e.printStackTrace(); } 26/01/2009 4
- 5. Query Execution Put the query as a string PREFIX my:<http://www.something.com/myontology#> PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?stud ?dip WHERE { ?stud my:enrolledIn } ?dip. String sparqlQuery = "PREFIX my:<http://www.something.com/myontology#>n" + "PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>n" + "n" + "SELECT ?stud ?dip n" + "WHERE {n" + " ?stud my:enrolledIn ?dip.n" + "} "; 26/01/2009 5
- 6. Query Execution Execute the Query encapsulates a parsed query read a textual query from a String Query query = QueryFactory.create(sparqlQuery); QueryExecution qe = QueryExecutionFactory.create(query, model); ResultSet results = qe.execSelect(); a single execution of a query 26/01/2009 6
- 7. Query Execution Print Query Results result set ResultSetFormatter.out(System.out, results, query); textual format standard output ----------------------------------| stud | dip | =================================== | my:Simon_Thevenin | my:M2_BDIA | | my:Raji_Ghawi | my:Doctorat | | my:Kamel_Boulil | my:M2_BDIA | ----------------------------------- 26/01/2009 output 7
- 8. XML format ResultSetFormatter.outputAsXML(System.out, results); 26/01/2009 <?xml version="1.0"?> <sparql xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:xs="http://www.w3.org/2001/XMLSchema#" xmlns="http://www.w3.org/2005/sparql-results#" > <head> <variable name="stud"/> <variable name="dip"/> </head> <results ordered="false" distinct="false"> <result> <binding name="stud"> <uri>http://www.something.com/myontology#Simon_Thevenin</uri> </binding> <binding name="dip"> <uri>http://www.something.com/myontology#M2_BDIA</uri> </binding> </result> <result> <binding name="stud"> <uri>http://www.something.com/myontology#Raji_Ghawi</uri> </binding> <binding name="dip"> <uri>http://www.something.com/myontology#Doctorat</uri> </binding> </result> <result> <binding name="stud"> <uri>http://www.something.com/myontology#Kamel_Boulil</uri> </binding> <binding name="dip"> <uri>http://www.something.com/myontology#M2_BDIA</uri> </binding> </result> </results> </sparql> output 8
- 9. Query Execution Save Query Results to String MyOutputStream myOutput = new MyOutputStream(); ResultSetFormatter.out(myOutput, results, query); String sparqlResults = myOutput.getString(); class MyOutputStream extends OutputStream { StringBuffer buf; public MyOutputStream(){ buf = new StringBuffer(); } public void write(int character) throws IOException { buf.append((char) character); } public String getString() { return buf.toString(); } } 26/01/2009 9
- 10. Query Execution Retrieve Query Solutions ResultSet results = qe.execSelect(); List vars = results.getResultVars(); while(results.hasNext()) { QuerySolution qs = results.nextSolution(); System.out.println("--------- solution ---------"); for (int i = 0; i < vars.size(); i++) { String var = vars.get(i).toString(); RDFNode node = qs.get(var); System.out.println(var + "t" + node.toString()); } } --------stud dip --------stud dip --------stud dip 26/01/2009 output solution --------http://www.something.com/myontology#Guillermo_Gomez http://www.something.com/myontology#These solution --------http://www.something.com/myontology#Elie_Raad http://www.something.com/myontology#M2-BDIA solution --------http://www.something.com/myontology#Raji_Ghawi http://www.something.com/myontology#M2-BDIA 10
- 11. ResultSet results = qe.execSelect(); List vars = results.getResultVars(); PrefixMapping pm = query.getPrefixMapping(); while (results.hasNext()) { QuerySolution qs = results.nextSolution(); System.out.println("--------- solution ---------"); for (int i = 0; i < vars.size(); i++) { String var = vars.get(i).toString(); RDFNode node = qs.get(var); String text = ""; if(node.isURIResource()){ text = pm.shortForm(node.asNode().getURI()); } else { text = node.toString(); } System.out.println(var+"t"+text); } } --------stud dip --------stud dip --------stud dip 26/01/2009 solution --------my:Guillermo_Gomez my:These solution --------my:Elie_Raad my:M2-BDIA solution --------my:Raji_Ghawi my:M2-BDIA output 11
- 13. Query Analysis PREFIX my:<http://www.something.com/myontology#> PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?stud ?modName WHERE { ?stud rdf:type my:Student . ?stud my:enrolledIn ?dip . ?dip my:hasModule ?mod . ?mod my:moduleName ?modName. FILTER (?modName='Databases'). } 26/01/2009 13
- 14. Query Analysis Put the Query in a String String sparqlQuery = "PREFIX my:<http://www.something.com/myontology#>n" + "PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>n" + "n" + "SELECT ?stud ?modName n" + "WHERE {n" + " ?stud rdf:type my:Student .n" + " ?stud my:enrolledIn ?dip .n" + " ?dip my:hasModule ?mod .n" + " ?mod my:moduleName ?modName.n" + " FILTER(?modName='Databases').n" + "} "; 26/01/2009 14
- 15. Query Analysis Create the Query Query query = QueryFactory.create(sparqlQuery); System.out.println("---------- Query System.out.println(query); ----------"); output ---------- Query ---------PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX my: <http://www.something.com/myontology#> SELECT ?stud ?modName WHERE { ?stud my:enrolledIn ?dip ; rdf:type my:Student ; my:enrolledIn ?dip . ?dip my:hasModule ?mod . ?mod my:moduleName ?modName . FILTER ( ?modName = "Databases" ) } 26/01/2009 15
- 16. Query Analysis Prefix Mapping System.out.println("------ Prefix Mapping ------"); Map map = query.getPrefixMapping().getNsPrefixMap(); Iterator pmIter= map.entrySet().iterator(); while (pmIter.hasNext()) { Entry ent = (Entry) pmIter.next(); String prefix = ent.getKey().toString(); String namespace = ent.getValue().toString(); System.out.println(prefix+"t"+namespace); } ------ Prefix Mapping -----rdf http://www.w3.org/1999/02/22-rdf-syntax-ns# my http://www.something.com/myontology# 26/01/2009 output 16
- 17. Query Analysis Retrieve Result Variables System.out.println("------ Result Variables ------"); List varList = query.getResultVars(); for (int i = 0; i < varList.size(); i++) { String var = varList.get(i).toString(); System.out.println(var); } ------ Result Variables -----stud modName output query.isQueryResultStar() query.isDistinct() 26/01/2009 17
- 18. Query Analysis Retrieve All Variables System.out.println("------- All Variables --------"); Iterator varIter = query.getQueryBlock().varsMentioned().iterator(); while(varIter.hasNext()){ String var = varIter.next().toString(); System.out.println(var); } ------- All Variables -------stud dip mod modName 26/01/2009 output 18
- 19. Query Analysis Fetch Query Elements ElementGroup eg = (ElementGroup) query.getQueryBlock().getPatternElement(); List elemList = eg.getElements(); for(int i=0; i<elemList.size(); i++){ Element elem = (Element) elemList.get(i); try{ if (elem instanceof ElementOptional) { ElementOptional elOp = (ElementOptional) elem; // .... } else if (elem instanceof ElementFilter) { ElementFilter elf = (ElementFilter) elem; // .... } else if (elem instanceof ElementTriplePattern) { ElementTriplePattern etp = (ElementTriplePattern) elem; // .... } } catch(ClassCastException e){ e.printStackTrace(); } } 26/01/2009 19
- 20. Query Analysis ElementOptional ElementOptional elOp = (ElementOptional) elem; Iterator iter = elOp.varsMentioned().iterator(); // .... ElementGroup newElemGrp = (ElementGroup) elOp.getElement(); List elemList = eg.getElements(); for(int i=0; i<elemList.size(); i++){ // .... } 26/01/2009 20
- 21. Query Analysis ElementFilter ElementFilter elf = (ElementFilter) elem; Iterator iter = elf.varsMentioned().iterator(); // .... Expr expr = elf.getConstraint().getExpr(); // .... 26/01/2009 21
- 22. Query Analysis Expr E_LogicalAnd E_LogicalOr E_Equals E_NotEquals E_LessThan E_LessThanOrEqual E_GreaterThan E_GreaterThanOrEqual E_LogicalNot getLeft() getRight() getSubExpr() E_Regex NodeVar if (expr instanceof E_LogicalAnd) { getVarName() E_LogicalAnd and = (E_LogicalAnd) expr; NodeValueInteger Expr left = and.getLeft(); NodeValueFloat Expr right = and.getRight(); asString() NodeValueDecimal // NodeValueString } else if (expr instanceof E_LogicalOr) { ... // .. .. } // .. .. else if (expr instanceof E_Regex) { E_Regex re = (E_Regex) expr; String pattern = ((NodeValueString) re.getPattern()).asString(); String varName = re.getRegexExpr().getVarName().toString(); // .. .. } 26/01/2009 22
- 23. Query Analysis ElementTriplePattern ElementTriplePattern etp = (ElementTriplePattern) elem; Triple triple = etp.getTriple(); Node subject = triple.getSubject(); Node predicate = triple.getPredicate(); Node object = triple.getObject(); SELECT ?stud ?dip WHERE { ?stud my:enrolledIn ?dip my:diplomaName } boolean isURI() boolean isLiteral() boolean isVariable() Subject Variable 26/01/2009 URI Predicate ?dip. "BDIA". Object Literal 23
- 25. Query Analysis OrderBy if(query.getOrderBy() != null){ Iterator orderBy = query.getOrderBy().iterator(); while (orderBy.hasNext()) { SortCondition sc = (SortCondition) orderBy.next(); Expr exp = sc.getExpression(); if(exp.isVariable()){ String obv = exp.getVarName(); // .... } } } 26/01/2009 25
- 26. References ARQ - A SPARQL Processor for Jena http://jena.sourceforge.net/ARQ/ Search RDF data with SPARQL http://www.ibm.com/developerworks/xml/library/j-sparql 26/01/2009 26