Apache Jena Part II Jan Pettersen Nytun, UiA 1 S O P This - PowerPoint PPT Presentation

Knowledge Representation Apache Jena Part II Jan Pettersen Nytun, UiA 1

S O P This presentation is based on: Jena Ontology API http://jena.apache.org/documentation/ontology/ Jan Pettersen Nytun, UIA, page 2

… Jena is fundamentally an RDF platform, … limited to ontology formalisms built on top of RDF. … this means RDFS, the varieties of OWL. 3

The OWL language is sub-divided into three syntax classes: OWL Lite , OWL DL and OWL Full . [Wikipedia]: • Every legal OWL Lite ontology is a legal OWL DL ontology. • Every legal OWL DL ontology is a legal OWL Full ontology. 4

[Wikipedia]: OWL Lite … intended to support those users primarily needing a classification hierarchy and simple constraints … Development of OWL Lite tools has … proven almost as difficult as development of tools for OWL DL, and OWL Lite is not widely used. 5

[Wikipedia]: OWL DL is designed to provide the maximum expressiveness possible while retaining computational completeness , decidability , and the availability of practical reasoning algorithms. OWL DL includes all OWL language constructs, but they can be used only under certain restrictions … 6

S [http://philosophy.stackexchange.com/questions/6992/ O P the-difference-between-soundness-and-completeness] • Soundness is the property of only being able to prove "true" things. • Completeness is the property of being able to prove all true things. • So a given logical system is sound if and only if the inference rules of the system admit only valid formulas. Or another way, if we start with valid premises, the inference rules do not allow an invalid conclusion to be drawn. • A system is complete if and only if all valid formula can be derived from the axioms and the inference rules. So there are no valid formula that we can't prove. • Together they imply that all and only validities are provable. Jan Pettersen Nytun, UIA, page 7

S Decidability O P [Wikipedia]: The logically valid formulas of a system are sometimes called the theorems of the system, … A logical system is decidable if there is an effective method for determining whether arbitrary formulas are theorems of the logical system. Jan Pettersen Nytun, UIA, page 8

S Gödel's incompleteness theorem O P [Wikipedia]: Recursively axiomatizable first-order theories that are rich enough to allow general mathematical reasoning to be formulated cannot be complete, as demonstrated by Gödel's incompleteness theorem. … For any such system, there will always be statements about the natural numbers that are true, but that are unprovable within the system. Jan Pettersen Nytun, UIA, page 9

[Wikipedia]: OWL Full [edit ] … a class can be treated simultaneously as a collection of individuals and as an individual in its own right ... OWL Full allows an ontology to augment the meaning of the pre-defined (RDF or OWL) vocabulary. OWL Full is undecidable, so no reasoning software is able to perform complete reasoning for it. 10

S Jena Graph Interface O P Graph is an internal Jena interface that supports the composition of sets of RDF triples. The asserted statements, which may have been read in from an ontology document, are held in the base graph. Jan Pettersen Nytun, UIA, page 11

S O P The reasoner, or inference engine, can use the contents of the base graph and the semantic rules of the language to show a more complete set of base and entailed triples. This is also presented via a Graph interface, so the OntModel works only with the outermost interface. Jan Pettersen Nytun, UIA, page 12

S O P The base graph can be an in- memory store, a database- backed persistent store, or some other storage structure altogether … Jan Pettersen Nytun, UIA, page 13

S Creating Ontology Models O P OntModel m = ModelFactory.createOntologyModel(); This will create an ontology model with the default settings: • OWL-Full language • in-memory storage • RDFS inference, which principally produces entailments from the sub-class and sub- property hierarchies. Jan Pettersen Nytun, UIA, page 14

S O P In many applications, such as driving a GUI, RDFS inference is too strong. An OWL model that performs no reasoning at all can be created with: OntModel m = ModelFactory.createOntologyModel( OntModelSpec.OWL_MEM ); Jan Pettersen Nytun, UIA, page 15

S O P Jan Pettersen Nytun, UIA, page 16

Testing Reasoning in Jena S O P Input Ontology @prefix : <http://www.uia.no/janpettersennytun/inference#> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix owl: <http://www.w3.org/2002/07/owl#> . @prefix xml: <http://www.w3.org/XML/1998/namespace> . @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . :hasApprovedId a owl:DatatypeProperty ; rdfs:subPropertyOf :hasSomeId . :hasSomeId a owl:DatatypeProperty . :hasHusband a owl:ObjectProperty ; owl:inverseOf :hasWife . :hasWife a owl:ObjectProperty . :Man a owl:Class ; rdfs:subClassOf :Human . :Woman a owl:Class ; rdfs:subClassOf :Human . :Human a owl:Class . :Homer a owl:NamedIndividual , :Man ; :hasSomeId "Homer_ID1_SomeID" . :Marge a owl:NamedIndividual , :Woman ; :hasApprovedId "Marge_ID1_Approved" ; :hasHusband :Homer . Jan Pettersen Nytun, UIA, page 17

S Testing Reasoning in Jena O P Application Heading package testreasoners; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.InputStream; import java.io.OutputStream; import java.util.ArrayList; import java.util.Collections; import java.util.List; import org.apache.jena.ontology.OntModel; import org.apache.jena.ontology.OntModelSpec; import org.apache.jena.rdf.model.Model; import org.apache.jena.rdf.model.ModelFactory; import org.apache.jena.rdf.model.Property; import org.apache.jena.rdf.model.RDFNode; import org.apache.jena.rdf.model.Resource; import org.apache.jena.rdf.model.Statement; import org.apache.jena.rdf.model.StmtIterator; import org.apache.jena.util.FileManager; Jan Pettersen Nytun, UIA, page 18

S Testing Reasoning in Jena O P Method Overview public class TestReasoners { private static String inputFileName = "InferenceTest__InputFile.ttl"; private static String outputFileName = "InferenceTest__OutputFile.ttl"; public static void main(String[] args ){ … } public static List<String> getSortedTriples(Model model ){ … } public static OntModel readFile(OntModelSpec ontModelSpec ){ … } } Jan Pettersen Nytun, UIA, page 19

S Testing Reasoning in Jena O P readFile - Method public static OntModel readFile(OntModelSpec ontModelSpec){ OntModel ontModel = ModelFactory.createOntologyModel(ontModelSpec); InputStream in = FileManager.get().open( inputFileName ); if (in == null) { System.out.println("File: " + inputFileName + " not found"); System.exit(1); } // read the Turtle file ontModel.read(in, null, "Turtle"); //ontModel.write(System.out, "Turtle"); return ontModel; } Jan Pettersen Nytun, UIA, page 20

S Testing Reasoning in Jena O P getSortedTriples- Method public static List<String> getSortedTriples(Model model){ List<String> triples = new ArrayList<String>(); StmtIterator iter = model.listStatements(); String format = "%-20s"; String defaultNamespace = model.getNsPrefixMap().get(""); if (defaultNamespace == null) return triples; Jan Pettersen Nytun, UIA, page 21

while (iter.hasNext()) { Statement stmt = iter.nextStatement(); // get next statement Resource subject = stmt.getSubject(); // get the subject String namespace = subject.getNameSpace(); if (namespace == null || !namespace.equals(defaultNamespace)) continue; Property predicate = stmt.getPredicate(); // get the predicate RDFNode object = stmt.getObject(); // get the object String tripleAsString = String.format(format, subject.getLocalName().toString()); tripleAsString = tripleAsString + String.format(format, predicate.getLocalName().toString()); if (object instanceof Resource) { tripleAsString = tripleAsString + object.asResource().getLocalName().toString() + " ."; } else { // object is a literal tripleAsString = tripleAsString + " \"" + object.toString() + "\"" + " ."; } triples.add(tripleAsString); } Collections.sort(triples); return triples; } Jan Pettersen Nytun, UIA, page 22

S O P public static void main(String[] args){ OntModel model_OWL_DL_MEM = readFile(OntModelSpec.OWL_DL_MEM); List<String> triples_OWL_DL_MEM = getSortedTriples(model_OWL_DL_MEM); System.out.println("Triple found in model_OWL_DL_MEM"); System.out.println("............................................................................."); for (String oneTriple : triples_OWL_DL_MEM) System.out.println(oneTriple); System.out.println(".............................................................................\n"); model_OWL_DL_MEM.close(); … Jan Pettersen Nytun, UIA, page 23