Using Java in Linked Data Applications - PowerPoint Presentation

Slide1

Using Java in Linked Data Applications

Fuming Shih

Oct 12Slide2

Java Libraries

Jena -

Java API for semantic web applications

Jastor

–

typesafe

, Ontology Driven RDF Access from Java

http://

jastor.sourceforge.net

/Slide3

Jena

P

rogrammatic 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 graphSlide4

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);Slide5

Task today

Load

Lalana’s

foaf

file at

http

://www.csail.mit.edu/~lkagal/foafExtract her friendsLook at the friends’ FOAF filesSee where they workUse 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 locatedSlide6

Installation

Download JDK

Download and install Eclipse

Download Jena and

Jastor

library

Tuning your Eclipse

Create a java projectAppend Jena & Jastor libraries to your classpathSlide7

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

);

….Slide8

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 caresSlide9

SW for JAVA P

rogrammer

RDF DB

Ontology files

Mapping tool

Jena2 Platform

(RDF model + Reasoning Engine + Persistence System)

JAVA VM

Java Objects

listener

Operator

FOAF

iCal

SIOC

Tag

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 ontologySlide10

Code

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

();

Tag tag =

edu.mit.dig.model.Tag.tagFactory.

createTag(NS_PREFIX

+ "id_1", model);

tag.addName("A

tag");

tag.addX(45);

tag.addY(32);

Create mapping

Make use of the classSlide11

Demo