Java and SPARQL

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

Raji GHAWI
26/01/2009

Outline



Query Execution



Query Analysis

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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();
}

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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" +
"} ";

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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

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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 |
-----------------------------------

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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();
}
}
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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').
}

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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" +
"} ";

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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" )
}
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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#

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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()
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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();
}
}

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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++){
// ....
}

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

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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();
// .. ..
}
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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

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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();
// ....
}
}
}

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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

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26

Java and SPARQL

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