The document discusses processing OWL ontologies using the Jena ontology API in Java. It describes how to create an ontology model, read an existing ontology, retrieve classes and properties, and examine class and property hierarchies. Key points include getting ontology classes and iterating over them, examining class relationships and restrictions, retrieving object and datatype properties, and getting property domains and ranges. The document provides examples of working with ontologies using the Jena API in Java.

1. Processing OWL Ontologies using Java
Jena Ontology API
Raji GHAWI
30/03/2010

2. Outline


What is Jena ?
Reading an Existing Ontology




Classes
Properties
Individuals
Creating a New Ontology



30/03/2010
Classes
Properties
Individuales
2

3. What is Jena ?

Jena is a Java framework


for building Semantic Web applications
includes






30/03/2010
an RDF API
reading and writing RDF in RDF/XML, N3 and N-Triples
an OWL API
in-memory and persistent storage
SPARQL query engine
http://jena.sourceforge.net/
3

4. Example Ontology
Person
name
age
email
Professor
Student
Class
studentNumber
subClassOf
Object property
taughtBy
teach
Datatype property
enrolledIn
hasModule
Module
moduleName
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Diploma
diplomaName
4

5. Outline


What is Jena ?
Reading an Existing Ontology




Classes
Properties
Individuals
Creating a New Ontology



30/03/2010
Classes
Properties
Individuales
5

6. Create Ontology Model

Jena provides an ontology model that allows to specify:



Ontology language
Storage model
Inference mode
OntModel model = ModelFactory.createOntologyModel();

default settings:



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OWL-Full language
in-memory storage
RDFS inference
6

7. OntModel model = ModelFactory.createOntologyModel(OntModelSpec.OWL_DL_MEM);
OntModelSpec
Language profile
Storage model
Reasoner
OWL_MEM
OWL full
in-memory
none
OWL_MEM_TRANS_INF
OWL full
in-memory
transitive class-hierarchy inference
OWL_MEM_RULE_INF
OWL full
in-memory
rule-based reasoner with OWL rules
OWL_MEM_MICRO_RULE_INF
OWL full
in-memory
optimised rule-based reasoner with OWL rules
OWL_MEM_MINI_RULE_INF
OWL full
in-memory
rule-based reasoner with subset of OWL rules
OWL_DL_MEM
OWL DL
in-memory
none
OWL_DL_MEM_RDFS_INF
OWL DL
in-memory
rule reasoner with RDFS-level entailment-rules
OWL_DL_MEM_TRANS_INF
OWL DL
in-memory
transitive class-hierarchy inference
OWL_DL_MEM_RULE_INF
OWL DL
in-memory
rule-based reasoner with OWL rules
OWL_LITE_MEM
OWL Lite
in-memory
none
OWL_LITE_MEM_TRANS_INF
OWL Lite
in-memory
transitive class-hierarchy inference
OWL_LITE_MEM_RDFS_INF
OWL Lite
in-memory
rule reasoner with RDFS-level entailment-rules
OWL_LITE_MEM_RULES_INF
OWL Lite
in-memory
rule-based reasoner with OWL rules
DAML_MEM
DAML+OIL
in-memory
none
DAML_MEM_TRANS_INF
DAML+OIL
in-memory
transitive class-hierarchy inference
DAML_MEM_RDFS_INF
DAML+OIL
in-memory
rule reasoner with RDFS-level entailment-rules
DAML_MEM_RULE_INF
DAML+OIL
in-memory
rule-based reasoner with DAML rules
RDFS_MEM
RDFS
in-memory
none
RDFS_MEM_TRANS_INF
RDFS
in-memory
transitive class-hierarchy inference
RDFS_MEM_RDFS_INF
RDFS
in-memory
rule reasoner with RDFS-level entailment-rules
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8. Read a File into Ontology Model
String fileName = "univ.owl";
try {
File file = new File(fileName);
FileReader reader = new FileReader(file);
OntModel model = ModelFactory
.createOntologyModel(OntModelSpec.OWL_DL_MEM);
model.read(reader,null);
model.write(System.out,"RDF/XML-ABBREV");
} catch (Exception e) {
e.printStackTrace();
}
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8

9. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Retrieve Ontology Classes
Iterator classIter = model.listClasses();
while (classIter.hasNext()) {
OntClass ontClass = (OntClass) classIter.next();
String uri = ontClass.getURI();
if(uri != null)
System.out.println(uri);
}


We can also use ontClass.getLocalName() to get the class name only.
If a class has no name (e.g. a restriction class), then ontClass.getURI()
returns null.
http://www.something.com/myontology#Professor
http://www.something.com/myontology#Module
http://www.something.com/myontology#Diploma
http://www.something.com/myontology#Person
http://www.something.com/myontology#Student
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output
9

10. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Retrieve a Specified Class

A specifed class is called by its URI
String classURI = "http://www.something.com/myontology#Professor";
OntClass professor = model.getOntClass(classURI );
// ...

If we know the class name only, we can get its URI by concatenating the
ontology URI with the class name:
ClassURI = OntologyURI + ‘#’ + ClassName
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10

11. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Get the Ontology URI
String ontologyURI = null;
Iterator iter = model.listOntologies();
if(iter.hasNext()){
Ontology onto = (Ontology) iter.next();
ontologyURI = onto.getURI();
System.out.println("Ontology URI = "+ontologyURI);
}
String className = "Professor";
String classURI = ontologyURI+"#"+className;
OntClass professor = model.getOntClass(classURI );
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11

12. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Class Hierarchy
OntClass student = model.getOntClass(uri+"#Student");
System.out.println(student.getSuperClass());
System.out.println(student.getSubClass());
http://www.something.com/myontology#Person
null
OntClass person = model.getOntClass(uri+"#Person");
System.out.println(person.getSuperClass());
System.out.println(person.getSubClass());
null
http://www.something.com/myontology#Professor
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12

13. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Class Hierarchy
Iterator supIter = person.listSuperClasses();
while (supIter.hasNext()) {
OntClass sup = (OntClass) supIter.next();
System.out.println(sup);
}
System.out.println("----------------");
Iterator subIter = person.listSubClasses();
while (subIter.hasNext()) {
OntClass sub = (OntClass) subIter.next();
System.out.println(sub);
}
---------------http://www.something.com/myontology#Professor
http://www.something.com/myontology#Student
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13

14. Reading an Existing Ontology
Creating a New Ontology
Classes
Properties
Individuales
Class Hierarchy
true
direct sub-classes
false
all sub-classes (default)
true
direct super-classes
false
all super-classes (default)
listSubClasses(boolean)
listSuperClasses(boolean)
A
B, C
->
B, C, D
D.listSuperClasses(true)
->
C
C
D
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->
A.listSubClasses(false)
B
A.listSubClasses(true)
D.listSuperClasses(false) ->
C, A
14

15. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Class Hierarchy
<OntClass>.isHierarchyRoot()

This function returns true if this class is the root of the class
hierarchy in the model:


this class has owl:Thing as a direct super-class,
or it has no declared super-classes
owl:Thing
Professor
Person
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Module
Diploma
Student
15

16. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Intersection / Union / Complement
if(ontClass.isIntersectionClass()){
IntersectionClass intersection = ontClass.asIntersectionClass();
RDFList operands = intersection.getOperands();
for (int i = 0; i < operands.size(); i++) {
RDFNode rdfNode = operands.get(i);
...
}
} else if(ontClass.isUnionClass()){
UnionClass union = ontClass.asUnionClass();
RDFList operands = union.getOperands();
...
} else if(ontClass.isComplementClass()){
ComplementClass compl = ontClass.asComplementClass();
RDFList operands = compl.getOperands();
...
}
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17. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Retrieve the Properties of a Specified Class
OntClass student = model.getOntClass(uri+"#Student");
Iterator propIter = student.listDeclaredProperties();
while (propIter.hasNext()) {
OntProperty property = (OntProperty) propIter.next();
System.out.println(property.getLocalName());
}
output
studentNumber
age
personName
enrolledIn
email
true
directly associated properties
false
all properties (direct + inhereted)
listDeclaredProperties(boolean)
(default)
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17

18. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Property Types

1
Two ways to know whether a property is datatype property or
object property:
if(property.isObjectProperty()){
// ... this is an object property
} else if (property.isDatatypeProperty()){
// ... this is an datatype property
}
property.isFunctionalProperty();
property.isSymmetricProperty();
property.isTransitiveProperty();
property.isInverseOf(anotherProperty);
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19. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Property Types

Two ways to know whether a property is datatype property or
object property:
Resource propertyType = property.getRDFType();
System.out.println(propertyType);
2
if(propertyType.equals(OWL.DatatypeProperty)){
// ... this is an datatype property
} else if(propertyType.equals(OWL.ObjectProperty)){
// ... this is an object property
}
http://www.w3.org/2002/07/owl#DatatypeProperty
http://www.w3.org/2002/07/owl#DatatypeProperty
http://www.w3.org/2002/07/owl#DatatypeProperty
http://www.w3.org/2002/07/owl#ObjectProperty
http://www.w3.org/2002/07/owl#DatatypeProperty
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output
19

20. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Property Domain and Range
String propertyName = property.getLocalName();
String dom = "";
String rng = "";
if(property.getDomain()!=null)
dom = property.getDomain().getLocalName();
if(property.getRange()!=null)
rng = property.getRange().getLocalName();
System.out.println(propertyName +": t("+dom+") t -> ("+rng+") ");
listDeclaredProperties(boolean);
true
studentNumber:
enrolledIn:
(Student)
(Student)
false
studentNumber:
age:
personName:
enrolledIn:
email:
(Student)
(Person)
(Person)
(Student)
(Person)
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-> (string)
-> (Diploma)
->
->
->
->
->
output
(string)
(int)
(string)
(Diploma)
(string)
20

21. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Datatype Properties

list all datatype properties in the model:
Iterator iter = model.listDatatypeProperties();
while (iter.hasNext()) {
DatatypeProperty prop = (DatatypeProperty) iter.next();
String propName = prop.getLocalName();
String dom = "";
String rng = "";
if(prop.getDomain()!=null)
dom = prop.getDomain().getLocalName();
if(prop.getRange()!=null)
rng = prop.getRange().getLocalName();
System.out.println(propName +": t("+dom+") t -> ("+rng+") ");
}
diplomaName:
studentNumber:
moduleName:
age:
personName:
email:
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(Diploma)
(Student)
(Module)
(Person)
(Person)
(Person)
-> (string)
-> (string)
-> (string)
-> (int)
-> (string)
-> (string)
output
21

22. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Object Properties

list all object properties in the model:
Iterator iter = model.listObjectProperties();
while (iter.hasNext()) {
ObjectProperty prop = (ObjectProperty) iter.next();
String propName = prop.getLocalName();
String dom = "";
String rng = "";
if(prop.getDomain()!=null)
dom = prop.getDomain().getLocalName();
if(prop.getRange()!=null)
rng = prop.getRange().getLocalName();
System.out.println(propName +": t("+dom+") t -> ("+rng+") ");
}
enrolledIn:
hasModule:
taughtBy:
teach:
(Student) -> (Diploma)
(Diploma) -> (Module)
(Module) -> (Professor)
(Professor) -> (Module)
getInverse()
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→
output
(OntProperty)
22

23. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Other Types of Properties

Using the same way, we may list (iterate) other properties:
model.listFunctionalProperties()
model.listInverseFunctionalProperties()
model.listSymmetricProperties()
model.listTransitiveProperties()
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23

24. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Restrictions
if(ontClass.isRestriction()){
Restriction rest = ontClass.asRestriction();
OntProperty onProperty = rest.getOnProperty();
...
}
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24

25. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
AllValuesFrom / SomeValuesFrom
if(rest.isAllValuesFromRestriction()){
AllValuesFromRestriction avfr = rest.asAllValuesFromRestriction();
Resource avf = avfr.getAllValuesFrom();
...
}
if(rest.isSomeValuesFromRestriction()){
SomeValuesFromRestriction svfr = rest.asSomeValuesFromRestriction();
Resource svf = svfr.getSomeValuesFrom();
...
}
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25

26. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
HasValue
if(rest.isHasValueRestriction()){
HasValueRestriction hvr = rest.asHasValueRestriction();
RDFNode hv = hvr.getHasValue();
...
}
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26

27. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Cardinality / MinCardinality / MaxCardinality
if(rest.isCardinalityRestriction()){
CardinalityRestriction cr = rest.asCardinalityRestriction();
int card = cr.getCardinality();
...
}
if(rest.isMinCardinalityRestriction()){
MinCardinalityRestriction mcr = rest.asMinCardinalityRestriction();
int minCard = minCR.getMinCardinality();
...
}
if(rest.isMaxCardinalityRestriction()){
MaxCardinalityRestriction mcr = rest.asMaxCardinalityRestriction();
int maxCard = maxCR.getMaxCardinality();
...
}
30/03/2010
27

28. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Individuals

list all individuals in the model
Iterator individuals = model.listIndividuals();
while (individuals.hasNext()) {
Individual individual = (Individual) individuals.next();
...
}

list individuals of a specific class
Iterator iter = ontClass.listInstances();
while (iter.hasNext()) {
Individual individual = (Individual) iter.next();
...
}
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28

29. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Individuals

list properties and property values of an individual
Iterator props = individual.listProperties();
while (props.hasNext()) {
Property property = (Property) props.next();
RDFNode value = individual.getPropertyValue(property);
...
}

list values of a specific property of an individual
Iterator values = individual.listPropertyValues(property);
while (values.hasNext()) {
RDFNode value = values.next();
...
}
30/03/2010
29

30. Reading an Existing Ontology
Classes
Creating a New Ontology
Properties
Individuales
Individuals

get the class to which an individual belongs
Resource rdfType = individual.getRDFType();
OntClass ontClass = model.getOntClass(rdfType.getURI());

in recent versions of Jena
OntClass ontClass = individual.getOntClass();
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30

31. Outline


What is Jena ?
Reading an Existing Ontology




Classes
Properties
Individuals
Creating a New Ontology



30/03/2010
Classes
Properties
Individuales
31

32. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Create the ontology model
OntModel model =
ModelFactory.createOntologyModel(OntModelSpec.OWL_DL_MEM);
String uriBase = "http://www.something.com/myontology";
model.createOntology(uriBase);
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32

33. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Create Classes
//create
OntClass
OntClass
OntClass
OntClass
OntClass
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classes
person = model.createClass(uriBase+"#Person");
module = model.createClass(uriBase+"#Module");
diploma = model.createClass(uriBase+"#Diploma");
student = model.createClass(uriBase+"#Student");
professor = model.createClass(uriBase+"#Professor");
33

34. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Set Sub-Classes
//set sub-classes
person.addSubClass(student);
person.addSubClass(professor);
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34

35. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Intersection / Union / Complement
RDFNode[] classes = new RDFNode[] {class1, class2, ...};
RDFList list = model.createList(classes);
IntersectionClass intersection =
model.createIntersectionClass(uri, list);
UnionClass union = model.createUnionClass(uri, list);
ComplementClass compl =
model.createComplementClass(uri, resource);
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35

36. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Create Datatype Properties
//create datatype properties
DatatypeProperty personName =
model.createDatatypeProperty(uriBase+"#personName");
personName.setDomain(person);
personName.setRange(XSD.xstring);
DatatypeProperty age = model.createDatatypeProperty(uriBase+"#age");
age.setDomain(person);
age.setRange(XSD.integer);
//
... ...
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36

37. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Create Object Properties
//create object properties
ObjectProperty teach = model.createObjectProperty(uriBase+"#teach");
teach.setDomain(professor);
teach.setRange(module);
ObjectProperty taughtBy =
model.createObjectProperty(uriBase+"#taughtBy");
taughtBy.setDomain(module);
taughtBy.setRange(professor);
ObjectProperty enrolledIn =
model.createObjectProperty(uriBase+"#enrolledIn");
enrolledIn.setDomain(student);
enrolledIn.setRange(diploma);
// ... ...
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37

38. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Inverse-of / Functional

set inverse properties
// set inverse properties
teach.setInverseOf(taughtBy);

set functional properties
// set functional properties
enrolledIn.setRDFType(OWL.FunctionalProperty);
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38

39. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Restrictions
usually, null
usually, a class
SomeValuesFromRestriction svfr =
model.createSomeValuesFromRestriction(uri, property, resource);
AllValuesFromRestriction avfr =
model.createAllValuesFromRestriction(uri, property, resource);
HasValueRestriction hvr =
model.createHasValueRestriction(uri, property, rdfNode);
CardinalityRestriction cr =
model.createCardinalityRestriction(uri, property, int);
MinCardinalityRestriction min_cr =
model.createMinCardinalityRestriction(uri, property, int);
MaxCardinalityRestriction max_cr =
model.createMaxCardinalityRestriction(uri, property, int);
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39

40. Creating a New Ontology
Reading an Existing Ontology
Classes
Properties
Individuales
Individuales

create an individual
Individual indv = ontClass.createIndividual(uri);
or
Individual indv = model.createIndividual(uri, ontClass);

set a property value of an individual
indv.setPropertyValue(property, rdfNode);
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40

41. Write Ontology Model

write the model to standard output
// write out the model
model.write(System.out,"RDF/XML-ABBREV");

save the model to a string
StringWriter sw = new StringWriter();
model.write(sw, "RDF/XML-ABBREV");
String owlCode = sw.toString();
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41

42. Save the Model to a File
File file = new File(filePath);
try{
FileWriter fw = new FileWriter(file);
fw.write(owlCode);
fw.close();
} catch(FileNotFoundException fnfe){
fnfe.printStackTrace();
} catch(IOException ioe){
ioe.printStackTrace();
}
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42

43. References

Jena Ontology API


http://jena.sourceforge.net/ontology/index.html
RDFS and OWL Reasoning Capabilities:

http://www-ksl.stanford.edu/software/jtp/doc/owl-reasoning.html
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