Download Jena (Java)

Using Java in Linked Data
Applications
Fuming Shih
Oct 12
Java Libraries
• Jena - Java API for semantic web applications
• Jastor – typesafe, Ontology Driven RDF Access
from Java
– http://jastor.sourceforge.net/
Jena
• Programmatic environment for RDF, RDFS and
OWL, SPARQL and includes a rule-based
inference engine.
• Jena has :
– Resource interface  represent resources
– Property interface  represent properties
– Literal interface  represent literals
– Model interface  represent graph
Example code to create graph with
jena
// some definitions
static String personURI =
"http://somewhere/JohnSmith";
static String fullName = "John Smith";
// create an empty Model
Model model = ModelFactory.createDefaultModel();
// create the resource
Resource johnSmith =
model.createResource(personURI);
// add the property
johnSmith.addProperty(VCARD.FN, fullName);
Task today
• Load Lalana’s foaf file at
http://www.csail.mit.edu/~lkagal/foaf
• Extract her friends
• Look at the friends’ FOAF files
• See where they work
• Use the workplace URI or the labels to query
dbpedia for it’s location
• Print a list of friends, their workplaces and where
the workplaces are located
Installation
1.
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Download JDK
Download and install Eclipse
Download Jena and Jastor library
Tuning your Eclipse
Create a java project
Append Jena & Jastor libraries to your
classpath
Code
Model model = ModelFactory.createDefaultModel();
// read the RDF/XML file
model.read("http://www.csail.mit.edu/~lkagal/foaf", null);
Property p_friend = model.createProperty("http://xmlns.com/foaf/0.1/knows");
StmtIterator friends = model.listStatements(null, p_friend, (RDFNode)null);
while(friends.hasNext()){
Resource friend = (Resource) (friends.nextStatement().getObject());
Model model_friend = ModelFactory.createDefaultModel();
try{
model_friend.read(friend.getURI(),null);
StmtIterator workPages =
model_friend.listStatements(null, workPlaceHomepage,(RDFNode) null);
while(workPages.hasNext()){
String workPlace = workPages.nextStatement().getObject().toString();
queryWorkPlace(friend.getURI(), workPlace);
….
From Protégé to Java Objects
• From ontology engineering to writing
Semantic Web application is not
straightforward
• Graph is fundamentally not intuitive to
programmer
• Save your time by choosing the right tools
• But be aware that mapping from OO to
ontology needs cares
SW for JAVA Programmer
• Using ontology to represent domain knowledge
– Use protégé to create/import different domain ontologies
• Mapping ontologies to JAVA classes
– Use Jastor library to generates Java interfaces, implementations, factories, and
listeners based on the properties and class hierarchies in the Web ontologies
– Easier for non-Semantic Web java developer to make use of ontology
Java Objects
iCal
SIOC
Tag
FOAF
listener
Operator
Mapping
tool
Jena2 Platform
(RDF model + Reasoning Engine +
Persistence System)
Ontology
files
JAVA VM
RDF DB
Code
Create mapping
JastorContext ctx = new JastorContext();
ctx.addOntologyToGenerate(new FileInputStream("src/data/Tag.owl"),
"http://www.mit.edu/dig/ns/tag",
"edu.mit.dig.model.Tag");
JastorGenerator gen = new JastorGenerator(
new File("gensrc").getCanonicalFile(),
ctx);
gen.run();
Make use of the class
Tag tag = edu.mit.dig.model.Tag.tagFactory.createTag(NS_PREFIX + "id_1", model);
tag.addName("A tag");
tag.addX(45);
tag.addY(32);
Demo