Presentation for the tutorial on Semantic Modelling using Semantic Web Technology for the XML Holland community.

1. Semantic Modelling WorkshopSemantic Web Technology RinkeHoekstrahoekstra@few.vu.nl Semantic Web Rubik's Cube by dullhunk at flickr under a cc-license. Thanks!

3. Overview Semantic Web: background Ideology Semantic Web and Linked Data Knowledge Representation and Ontology Quick overview RDF and RDFS OWL 2 DL SKOS SPARQL Resources Wrap Up Tutorial information

4. Background Information The Web as a Knowledge Base

5. The Semantic Web Ideology Identity is everything Partial solutions are great too! Layer cake/Web Stack 2/22/10 5 OWL

6. Key Aspects World Wide Web Consortium Globally unique identifiers URI and IRI Straightforward data integration Interdependent languages Resource Description Framework (RDF) RDF Schema (RDFS) Web Ontology Language (OWL), and OWL 2 SPARQL Query Language for RDF (SPARQL) Semantic Web Rule Language (SWRL) Rule Interchange Format (RIF) Simple Knowledge Organization System (SKOS)

8. `Metadata’ for web pages

9. Since ~2006

10. `Web of Data’

11. Semantic web as data source in its own right

12. Linked Data

13. A ‘Databaseesque’ Web

14. RDF Triple stores

15. Common schema and identification mechanism

16. A single query language2/22/10 7

17. Linked Open Data 2/22/10 8

18. 2/22/10 9 November 2009: 13.1 Billion triples, 142 Million links

19. But… not just Web History Semantic Networks and Frame Systems (‘70-ies) Formal Knowledge Representation (KL-One) Description Logics (DL) Model Theoretic Semantics Logic programming Strongly based in methodology Knowledge sharing and reuse Ontologies Formal semantics

20. Why Ontology? Knowledge bases that mix procedural and declarative knowledge are extremely hard to reuse Ontologies capture the `domain theory’ of a KBS: that what a KBS knows about Procedures capture what a KBS does with that knowledge Problem Solving Methods Slight problem: Rules look like procedures, but can also capture declarative knowledge

21. Why Formal Semantics? Standard inferences, dependable reasoning Reusable KBS components should guarantee: Soundnessall answers given should be correct Completenessthe system should give all answers Timelinessthe system should answer within reasonable time Consistencythe knowledge in a KB should be provably correct

22. WARNING Reasoners on the Semantic Web adopt the Open World Assumption as opposed to the Closed World Assumption of many other languages This means that: If a reasoner cannot infer that a conclusion holds, it stays silent, and will not report that it does not hold. This is contrary to the negation as failure (NAF) feature of many rule languages. Why? NAF hinders reusability on the Web because conclusions may change depending on new information.

23. Ingredients Ontology (TBox) Classesconcepts in the domain (≈ DB tables) Propertiesrelations that hold between individuals, or between an individual and a literal value (≈ DB columns) Axioms (only in OWL)restrictions on relations that may hold between instances of a certain class. Assertions (ABox) Individualsinstances of classes in the ontology (≈ DB records) Property assertionsrelations that hold between instances (≈ DB record entries) Rules

24. Architecture

25. Very Quick Overview Examples

26. Multiple Syntaxes RDF RDF/XMLVerbose, does not make an exact ‘fit’ with RDF data model TurtleHuman readable RDFaEmbedded in XHTML as attributes TriXSupports ‘named graphs’ OWL All RDF syntaxes, though RDF/XML is normative OWL XMLXSLT-able Functional SyntaxMapping to Structural Specification (UML MOF) Manchester SyntaxHuman readable, used by most editors (Protégé, TopBraid)

27. 2/22/10 18 URI’sand Namespaces URI: Universal Resource Identifier ... Just an identifier http://www.leibnizcenter.org/people#joost URL: Universal Resource Location http://www.leibnizcenter.org/people#joost URN: Universal Resource Name urn:leibnizcenter:people:joost Namespace A ‘space’ in which all locally defined names are unique, e.g.: http://www.leibnizcenter.org/people#joost http://www.hcs.science.uva.nl/staff#joost Basis for `trust’

29. Traverse subclass hierarchy

32. OWL 2 DL Reasoning Consistency and coherency checking Are all axioms and assertions consistent? Classification Determine subclass relations between classes Infer disjointness and equivalence of classes Realization Determine class membership for individuals Infer new property relations with other individuals

33. OWL 2 DL (1) owl:Thing and owl:Nothing Class axioms Intersection, union, disjointness, equivalence:Minister disjointWith:Kamerlid someValuesFrom (existential):Omnivore subClassOf:Animal and (:eats some :Vegetable) allValuesFrom (universal):Herbivore subClassOf:Animal and (:eats only :Vegetable) hasValue:CowsCalledBettyequivalentTo:Cow and (:name has “Betty”) Self:Narcissist equivalentTo:likes Self

34. OWL 2 DL (2) Class axioms (cont’d) (Qualified) Cardinality:Premier equivalentTo:is_premier_vanmin 1 :Kabinet:KabinetsubClassOf:heeft_premiermax 1 :Premier Property axioms Transitive, chains Inverse Functional, inverse functional Reflexive, irreflexive Symmetric, asymmetric Disjoint, equivalent Property types Object Property vs. Datatype Property

35. OWL 2 Profiles Subsets of OWL 2 syntax that have desirable computational properties OWL 2 QL Optimized for ontologies with many instances Query answering OWL 2 EL Optimized for ontologies with many classes OWL 2 RL Implementable using rule-based technology

36. Vocabularies RDFS and OWL 2 DL semantics often too much Simple method for describing taxonomies Simple Knowledge Organization System Lifting existing KOS’s to the Semantic Web Every skos:Concept is an OWL individual Lightweight semantic relations: broader, narrower, and related. Lightweight mapping relations between skos:ConceptSchemes. JURIX 2009

37. Querying: SPARQL RDF Repositories exposed via SPARQL Endpoints Query types SELECT … WHERE … CONSTRUCT … WHERE … ( similar to rules!) DELETE … WHERE … Example PREFIXr: <http://www.overheid.nl/regering#> PREFIXk: <http://www.overheid.nl/kabinet#> SELECT ?name WHERE { ?xr:is_premier_van k:balkenende_4. ?xr:name?name } ?xbinds with <http://www.overheid.nl/personen#balkenende> ?name binds with“Jan Peter Balkenende”^^xsd:string 2/22/10 27

38. Resources: Documentation W3C Semantic Web portalhttp://www.w3.org/standards/semanticweb/ Start with RDF Primerhttp://www.w3.org/TR/rdf-primer/ OWL2 Document Overview & Primerhttp://www.w3.org/TR/owl-overview/http://www.w3.org/TR/owl-primer/ SPARQLhttp://www.w3.org/TR/rdf-sparql-query/ SKOS Primerhttp://www.w3.org/TR/skos-primer/ Rule Interchange Formathttp://www.w3.org/2005/rules/wiki/RIF_Working_Group

39. Resources: Tools Editors TopBraid Composer (RDF+OWL) Protégé 4 (OWL Only) Reasoners Pellet, Fact++, OWLIM, Racer, HermiT, CEL RDF Repositories OpenRDF Sesame, 4Store/5Store, Virtuoso, Mulgara RDB to RDF bridges D2RQ

40. Wrap Up: Benefits Single `database schema’ eases query writing Global identifiers facilitate data integration Layered approach eases extensibility Formal semantics ensure dependability

41. Wrap Up: Tutorial Information 2 Hour session TopBraid Composer Standard (trial license) What we’ll do: Understanding an ontology & using a reasoner Data integration using SPARQL Simple OWL class definitions Advanced OWL class definitions (extra)