Scala Programming for Semantic Web Developers ESWC Semdev2015
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Scalable and Reactive Programming for Semantic Web Developers discusses using Scala for semantic web development. Key points include: - Scala allows for more concise RDF code compared to Java through features like type inference and implicit parameters. - The actor model and futures in Scala enable asynchronous and reactive programming for RDF streams and SPARQL queries. - OWL API reasoning with ontologies can be done more clearly in Scala through implicit classes that simplify common operations.
![Query with SPARQL
9
val queryStr = """select distinct ?Concept
where {[] a ?Concept} LIMIT 10"""
val query = sparql(queryStr)
query.serviceSelect("http://dbpedia.org/sparql").foreach{implicit qs=>
println(res("Concept").getURI)
}
val f=Future(query.serviceSelect("http://es.dbpedia.org/sparql")).fallbackTo(
Future(query.serviceSelect("http://dbpedia.org/sparql")))
f.recover{
case e=> println("Error "+e.getMessage)
}
f.map(_.foreach{implicit qs=>
println(res("Concept").getValue)
})
Remote SPARQL endpoint
Simplified access to
Query solutions
Futures: asnyc execution
Non blocking code
Fallback alternative execution](https://image.slidesharecdn.com/semdev2015jpc-150531163243-lva1-app6891/85/Scala-Programming-for-Semantic-Web-Developers-ESWC-Semdev2015-9-320.jpg)
![RDF Streams: Actors
12
val sys=ActorSystem.create("system")
val consumer=sys.actorOf(Props[RdfConsumer])
class Streamer extends StreamRDF{
override def triple(triple:Triple){
consumer ! triple
}
}
class RdfConsumer extends Actor{
def receive= {
case t:Triple =>
if (t.predicateMatches(RDF.‘type‘))
println(s"received triple $t")
}
RDF consumer
Actor receive method
Implements behavior
Message-passing model
RDF producer
Async message passing](https://image.slidesharecdn.com/semdev2015jpc-150531163243-lva1-app6891/85/Scala-Programming-for-Semantic-Web-Developers-ESWC-Semdev2015-12-320.jpg)
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Scala Programming for Semantic Web Developers ESWC Semdev2015
- 1. Scalable and Reactive Programming for Semantic Web Developers Jean-Paul Calbimonte LSIR EPFL Developers Workshop. Extended Semantic Web Conference ESWC 2015 Portoroz, 31.05.2015 @jpcik
- 2. Semantic Web Devs 2 Have fun Love challenges Need cool tools Sesame
- 3. Scala: Functions and Objects 3 JVM language Both object and functional oriented Easy Java-interop Reuse Java libraries Growing community
- 4. RDF in Jena: in Scala String personURI = "http://somewhere/JohnSmith"; Model model = ModelFactory.createDefaultModel(); model.createResource(personURI).addProperty(VCARD.FN,"John Smith"); Type inference Not too useful ; and () 4 Terser & compact code Type-safe DSL Compiler takes care val personURI = "http://somewhere/JohnSmith" val model = ModelFactory.createDefaultModel model.createResource(personURI).addProperty(VCARD.FN,"John Smith") sw:JohnSmith “John Smith” vcard:FN val personURI = "http://somewhere/JohnSmith" implicit val model = createDefaultModel add(personURI,VCARD.FN->"John Smith") boilerplate String converted to Resource
- 5. Some more RDF 5 String personURI = "http://somewhere/JohnSmith"; String givenName = "John"; String familyName = "Smith"; String fullName = givenName + " " + familyName; Model model = ModelFactory.createDefaultModel(); model.createResource(personURI) .addProperty(VCARD.FN,fullName) .addProperty(VCARD.N,model.createResource() .addProperty(VCARD.Given,givenName) .addProperty(VCARD.Family,familyName)); val personURI = "http://somewhere/JohnSmith" val givenName = "John" val familyName = "Smith" val fullName = s"$givenName $familyName" implicit val model = createDefaultModel add(personURI,VCARD.FN->fullName, VCARD.N ->add(bnode,VCARD.Given -> givenName, VCARD.Family->familyName)) sw:JohnSmith “John Smith” vcard:FN _:n “John” “Smith”vcard:N vcard:Given vcard:Family Blank node Scala DSLs customizable Predicate-objects are pairs
- 6. Some more RDF in Jena 6 implicit val m=createDefaultModel val ex="http://example.org/" val alice=iri(ex+"alice") val bob=iri(ex+"bob") val charlie=iri(ex+"charlie") alice+(RDF.`type`->FOAF.Person, FOAF.name->"Alice", FOAF.mbox- >iri("mailto:[email protected]"), FOAF.knows->bob, FOAF.knows->charlie, FOAF.knows->bnode) bob+ (FOAF.name->"Bob", FOAF.knows->charlie) charlie+(FOAF.name->"Charlie", FOAF.knows->alice) Still valid Jena RDF You can do it even nicer
- 7. Exploring an RDF Graph 7 ArrayList<String> names=new ArrayList<String>(); NodeIterator iter=model.listObjectsOfProperty(VCARD.N); while (iter.hasNext()){ RDFNode obj=iter.next(); if (obj.isResource()) names.add(obj.asResource() .getProperty(VCARD.Family).getObject().toString()); else if (obj.isLiteral()) names.add(obj.asLiteral().getString()); } val names=model.listObjectsOfProperty(VCARD.N).map{ case r:Resource=> r.getProperty(VCARD.Family).obj.toString case l:Literal=> l.getString } Imperative iteration of collections Type-based conditional execution Type casting Case type Map applied to operators
- 8. 8
- 9. Query with SPARQL 9 val queryStr = """select distinct ?Concept where {[] a ?Concept} LIMIT 10""" val query = sparql(queryStr) query.serviceSelect("http://dbpedia.org/sparql").foreach{implicit qs=> println(res("Concept").getURI) } val f=Future(query.serviceSelect("http://es.dbpedia.org/sparql")).fallbackTo( Future(query.serviceSelect("http://dbpedia.org/sparql"))) f.recover{ case e=> println("Error "+e.getMessage) } f.map(_.foreach{implicit qs=> println(res("Concept").getValue) }) Remote SPARQL endpoint Simplified access to Query solutions Futures: asnyc execution Non blocking code Fallback alternative execution
- 10. Actor Model 10 Actor 1 Actor 2 m No shared mutable state Avoid blocking operators Lightweight objects Loose coupling communicate through messages mailbox state behavior non-blocking response send: fire-forget Implementations: e.g. Akka for Java/Scala Pare nt Actor 1 Supervision hierarchy Supervision Actor 2 Actor 4 X Actor 2 Act or1 Act or2 m Act or3 Act or4 m m Remoting
- 11. Reactive Systems Event-Driven Jonas Boner. Go Reactive: Event-Driven, Scalable, Resilient & Responsive Systems. 2013. Events: reactto ScalableLoad: ResilientFailure: ResponsiveUsers: 11
- 12. RDF Streams: Actors 12 val sys=ActorSystem.create("system") val consumer=sys.actorOf(Props[RdfConsumer]) class Streamer extends StreamRDF{ override def triple(triple:Triple){ consumer ! triple } } class RdfConsumer extends Actor{ def receive= { case t:Triple => if (t.predicateMatches(RDF.‘type‘)) println(s"received triple $t") } RDF consumer Actor receive method Implements behavior Message-passing model RDF producer Async message passing
- 13. Web RDF Services 13 GET /containers/:containerid/ org.rsp.ldp.ContainerApp.retrieve(containerid:String) POST /containers/:containerid/ org.rsp.ldp.ContainerApp.add(containerid:String) object ContainerApp extends Controller { def retrieve(id:String) = Action.async {implicit request=> val sw=new StringWriter val statements=m.listStatements(iri(prefix+id+"/"),null,null) val model=createDefaultModel statements.foreach(i=>model.add(i)) model.write(sw, "TURTLE") Future(Ok(sw.toString).as("text/turtle").withHeaders( ETAG->tag, ALLOW->"GET,POST" )) } Routing rules Controller returns RDF async
- 14. OWLAPI: reasoning 14 val onto=mgr.createOntology val artist=clazz(pref+"Artist") val singer=clazz(pref +"Singer") onto += singer subClassOf artist val reasoner = new RELReasonerFactory.createReasoner(onto) val elvis=ind(pref+"Elvis") reasoner += elvis ofClass singer reasoner.reclassify reasoner.getIndividuals(artist) foreach{a=> println(a.getRepresentativeElement.getIRI) } Creating OWL classes Declaring class relationships Declare instances
- 15. How is it done? 15 object OwlApiTips{ implicit class TrowlRelReasoner(reasoner:RELReasoner){ def += (axiom:OWLAxiom)= reasoner.add(Set(axiom)) } implicit class OwlClassPlus(theClass:OWLClass){ def subClassOf(superclass:OWLClass)(implicit fac:OWLDataFactory)= fac.getOWLSubClassOfAxiom(theClass, superclass) } implicit class OwlOntologyPlus(onto:OWLOntology){ def += (axiom:OWLAxiom)(implicit mgr:OWLOntologyManager)= mgr.addAxiom(onto, axiom) } implicit class OwlIndividualPlus(ind:OWLIndividual){ def ofClass (theclass:OWLClass)(implicit fac:OWLDataFactory)= fac.getOWLClassAssertionAxiom(theclass, ind) } implicit def str2Iri(s:String):IRI=IRI.create(s) object clazz{ def apply(iri:String)(implicit fac:OWLDataFactory)= fac.getOWLClass(iri) } object ind{ def apply(iri:String)(implicit fac:OWLDataFactory)= fac.getOWLNamedIndividual(iri) } }
- 16. Muchas gracias! Jean-Paul Calbimonte LSIR EPFL @jpcik