Programming the Semantic Web

Programming the Semantic Web

• 1.
  Programming THE SEMANTIC WEB Buildan application upon Semantic Web models. Brief overview of Apache Jena and OWL-API.
• 2.
  Recap: Tools • Editors(http://semanticweb.org/wiki/Editors) – Most common editor: Protégé 5 – Other tools: TopBraid Composer ($), NeOn toolkit – Special purpose apps, esp. for light-weight ontologies (e.g., FOAF editors) • Reasoners (http://semanticweb.org/wiki/Reasoners) – OWL DL: Pellet 2.0*, HermiT, FaCT++, RacerPro ($) – OWL EL: CEL, SHER, snorocket ($), ELLY – OWL RL: OWLIM, Jena, Oracle OWL Reasoner ($) – OWL QL: Owlgres, QuOnto, Quill * The next-gen reasoner (version 3) is part of Stardog, a closed source RDF database 22/02/2017 Programming the Semantic Web 2
• 3.
  Recap: How tocreate an ontology 1. Determine the scope 2. Consider reuse 3. Enumerate terms 4. Define classes 5. Define properties 6. Define constraints 7. Create instances 22/02/2017 Programming the Semantic Web 3 Determine the scope Consider reuse Enumerate terms Define classes Define properties Define constraints Create instances
• 4.
  Now what? • Youcreated a OWL ontology… • … or you want to query some SPARQL endpoints… • How to do this programmatically? – e.g., from a software application • Good news: frameworks exist! – They are written in Java… – Apache Jena (RDF/SPARQL/…) – OWL API (OWL2) 22/02/2017 Programming the Semantic Web 4
• 5.
  Apache Jena • Freeand open source Java framework – for building Semantic Web and Linked Data applications – https://jena.apache.org • It is composed by several APIs – as well as command line tools 22/02/2017 Programming the Semantic Web 5
• 6.
  Apache Jena • Tutorialsavailable – https://jena.apache.org/tutorials/index.html – sample code: https://github.com/apache/jena/tree/master/jena- core/src-examples/jena/examples/rdf • It has a limited support to OWL 1.1 – no OWL2 – basically, do not use Jena for ontologies! 22/02/2017 Programming the Semantic Web 6
• 7.
  Creating a RDF… StringpersonURI = "http://somewhere/JohnSmith"; String givenName = "John"; String familyName = "Smith"; String fullName = givenName + " " + familyName; // create an empty model Model model = ModelFactory.createDefaultModel(); // create the resource and add the properties cascading style Resource johnSmith = model.createResource(personURI) .addProperty(VCARD.FN, fullName) .addProperty(VCARD.N, model.createResource() .addProperty(VCARD.Given, givenName) .addProperty(VCARD.Family, familyName)); 22/02/2017 Programming the Semantic Web 7
• 8.
  Writing RDF… • Writethe previous model on a OutputStream // now write the model in XML form to a file model.write(System.out); • You can also specify the format // you can also specify the format, e.g., // model.write(System.out, "TURTLE"); 22/02/2017 Programming the Semantic Web 8
• 9.
  Reading RDF… • Readfrom a InputStream String inputFileName = "vc-db-1.rdf"; InputStream in = FileManager.get().open(inputFileName); // read the RDF/XML file model.read(in, ""); 22/02/2017 Programming the Semantic Web 9 The base URI to be used when converting relative URI's to absolute URI's
• 10.
  SPARQL • Jena supportsSPARQL querying through the ARQ engine – Standard SPARQL – Free text search via Lucene – Access and extension of the SPARQL algebra – Property functions for custom processing of semantic relationships – Aggregation, GROUP BY and assignment as SPARQL extensions – Client-support for remote access to any SPARQL endpoint – … 22/02/2017 Programming the Semantic Web 10
• 11.
  SPARQL with ARQ [...] //Create a new query String queryString = "PREFIX foaf: <http://xmlns.com/foaf/0.1/> " + "SELECT ?url " + "WHERE {" + " ?contributor foaf:name "Luigi De Russis" . " + " ?contributor foaf:weblog ?url . " + " }"; Query query = QueryFactory.create(queryString); // Execute the query and obtain results QueryExecution qe = QueryExecutionFactory.create(query, model); ResultSet results = qe.execSelect(); // Output query results ResultSetFormatter.out(System.out, results, query); // Free up resources used running the query qe.close(); 22/02/2017 Programming the Semantic Web 11
• 12.
  OWL API • AJava API and reference implementation – for creating, manipulating and serializing OWL 2 Ontologies – http://owlcs.github.io/owlapi • Free and open source • Created and maintained by the University of Manchester – http://owl.cs.manchester.ac.uk 22/02/2017 Programming the Semantic Web 12
• 13.
  OWL API • Itincludes the following components – API for OWL 2 and an efficient in-memory reference implementation – RDF/XML parser and writer – OWL/XML parser and writer – OWL Functional Syntax parser and writer – Turtle parser and writer – SWRL – Reasoner interfaces • towards, e.g., FaCT++, HermiT, Pellet, and Racer 22/02/2017 Programming the Semantic Web 13
• 14.
  OWL API • Documentationand Javadocs – https://github.com/owlcs/owlapi/wiki – http://owlcs.github.io/owlapi/apidocs_4/index.html – scarce and not updated, sometimes • Versions – 5.0, cutting edge, Java 8 only – 4.0, stable, Java 7+ • currently used by Protégé • several examples are available, right now 22/02/2017 Programming the Semantic Web 14
• 15.
  OWL API Fundamentals •OWLOntology – an interface – modelling a set of logical and nonlogical OWLAxioms, with a name (an IRI) and convenience methods to retrieve such axioms • OWLEntity – anything that can be identified with an IRI, i.e., class names, data and object properties, named individuals, … 22/02/2017 Programming the Semantic Web 15
• 16.
  OWL API Fundamentals •OWLAxiom – the basic unity – TBox axioms describe relations between classes and class expressions (equivalence, subsumption, disjointness) – ABox axioms (assertions) describe relations between individuals and between individuals and classes/class expressions – RBox axioms describe relations between properties 22/02/2017 Programming the Semantic Web 16
• 17.
  Load (or create)an ontology… • Ontology creation OWLOntologyManager m = OWLManager.createOWLOntologyManager(); OWLOntology o = m.createOntology(example_iri); • Ontology loading OWLOntologyManager m = OWLManager.createOWLOntologyManager(); OWLOntology o = m.loadOntologyFromOntologyDocument(ont_iri); 22/02/2017 Programming the Semantic Web 17 a File or a IRI
• 18.
  Save an ontology… •Save in OWL/XML format m.saveOntology(ontology, new OWLXMLOntologyFormat(), file); • Save in RDF/XML format m.saveOntology(ontology, file); 22/02/2017 Programming the Semantic Web 18
• 19.
  Learning by Example •We are going to use the University ontology we developed few weeks ago • We would like to – load the ontology – compute logical inferences – ask for • university individuals • which degrees each university offers • which courses each degree offers • who is enrolled in those courses 22/02/2017 Programming the Semantic Web 19
• 20.
  We are goingto use… • Eclipse (neon) – https://www.eclipse.org/downloads/ • OWL API 4.2.8 • HermiT reasoner 1.3.8.413 – download from https://github.com/owlcs/owlapi/wiki/Reasoners,-OWL- API-Support,-papers-about-the-OWL-API • Gradle 3.4 – for handling the OWL API/HermiT set up and dependencies – https://gradle.org/ – Eclipse supports Gradle through the Buildship plugin 22/02/2017 Programming the Semantic Web 20
• 21.
  Questions? 01RRDIU SEMANTIC WEB LuigiDe Russis luigi.derussis@polito.it
• 22.
  License • This workis licensed under the Creative Commons “Attribution- NonCommercial-ShareAlike Unported (CC BY-NC-SA 3,0)” License. • You are free: – to Share - to copy, distribute and transmit the work – to Remix - to adapt the work • Under the following conditions: – Attribution - You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). – Noncommercial - You may not use this work for commercial purposes. – Share Alike - If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one. • To view a copy of this license, visit http://creativecommons.org/license/by-nc-sa/3.0/ 22/02/2017 Programming the Semantic Web 22