Java and SPARQL

Processing SPARQL Queries using Java
ARQ - A SPARQL Processor for Jena

Raji GHAWI
26/01/2009

Outline



Query Execution



Query Analysis

26/01/2009

2

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

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

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

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

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>
<uri>http://www.something.com/myontology#Raji_Ghawi</uri>
</binding>
<uri>http://www.something.com/myontology#Doctorat</uri>
</binding>
</result>
<result>
<uri>http://www.something.com/myontology#Kamel_Boulil</uri>
</binding>
<uri>http://www.something.com/myontology#M2_BDIA</uri>
</binding>
</result>
</results>
</sparql>

output

8

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

Query Execution
Retrieve Query Solutions
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

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

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

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

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

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

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

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

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

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

Query Analysis
ElementFilter
ElementFilter elf = (ElementFilter) elem;
Iterator iter = elf.varsMentioned().iterator();
// ....
Expr expr = elf.getConstraint().getExpr();
// ....

26/01/2009

21

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

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

Subject

Predicate

Object

URI

Literal
Variable

26/01/2009

24

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

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

Java and SPARQL

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (20)

Similar to Java and SPARQL

Similar to Java and SPARQL (20)

More from Raji Ghawi

More from Raji Ghawi (10)

Recently uploaded

Recently uploaded (20)

Java and SPARQL