seminar presentation

1. Seminar For Web Ontology Language (OWL) Prepared by: Hussein Ali Ahmad Ghanim 6/19/20112 1 WEB ONTOLOGY LANGUAGE (OWL)

2. Web Ontology Language: OWL Web Ontology Language Definition. Overview Requirements for ontology languages OWL Languages - OWL, RDF, RDF(s), XML References 6/19/20112 2 WEB ONTOLOGY LANGUAGE (OWL)

3. Web Ontology Language The Web Ontology Language (OWL) is a family of knowledge representation languages for authoring ontologies. The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web. Semantic Web led to requirement for a “web ontology language” 6/19/20112 3 WEB ONTOLOGY LANGUAGE (OWL)

4. Overview From the overview of OWL1: The OWL Web Ontology Language is designed for use by applications that need to process the content of information instead of just presenting information to humans. OWL facilitates greater machine interpretability of Web content than that supported by XML, RDF, and RDF Schema (RDF-S) by providing additional vocabulary along with a formal semantics. OWL has three increasingly-expressive sublanguages: OWL Lite, OWL DL, and OWL Full. 6/19/20112 4 WEB ONTOLOGY LANGUAGE (OWL)

5. Lite DL Full Three species of OWL Full: uses all the OWL languages primitives. It also allows to combine these primitives in arbitrary ways with RDF and RDF Schema. This includes the possibility to change the meaning of the pre-defined primitives, by applying the language primitives to each other. The advantage of OWL Full is that it is fully upward compatible with RDF, both syntactically and semantically. The disadvantage of OWL Full is the language has become so powerful as to be undecidable, dashing any hope of complete (let alone efficient) reasoning support. DL = Description Logicis a sublanguage of OWL Full which restricts the way in which the constructors from OWL and RDF can be used. The advantage of this is that it permits efficient reasoning support. The disadvantage is that we loose full compatibility with RDF. 6/19/20112 5 WEB ONTOLOGY LANGUAGE (OWL)

6. Three species of OWL Lite: - An ever further restriction limits OWL DL to a subset of the language constructors. For example, OWL Lite excludes enumerated classes, disjointness statements and arbitrary cardinality (among others). - The advantage of this is a language that is both easier to grasp (for users) and easier to implement (for tool builders). - The disadvantage is of course a restricted expressivity. 6/19/20112 6 WEB ONTOLOGY LANGUAGE (OWL)

7. Requirements for ontology languages Ontology languages allow users to write explicit, formal conceptualizations of domains models. The main requirements are: 1. a well-defined syntax 2. a well-defined semantics 3. efficient reasoning support 4. sufficient expressive power 5. convenience of expression. 6/19/20112 7 WEB ONTOLOGY LANGUAGE (OWL)

8. What is OWL? W3C Recommendation, February 2004. web standard Web Ontology Language built on top of RDF RDF: the Resource Description Framework is an XML-based language to describe resources. for processing information on the web designed to be interpreted by computers, not for being read by people OWL is written in XML 6/19/20112 8 WEB ONTOLOGY LANGUAGE (OWL)

9. Why OWL? OWL is a part of the "Semantic Web Vision" - a future where: Web information has exact meaning Web information can be processed by computers Computers can integrate information from the web OWL was designed to provide a common way to process the content of web information (instead of displaying it). be read by computer applications (instead of humans). 6/19/20112 9 WEB ONTOLOGY LANGUAGE (OWL)

11. These languages are then used to support the representation and use of metadata.

12. The languages provide basic machinery that we can use to represent the extra semantic information needed for the Semantic Web

13. XML

14. RDF

15. RDF(S)

16. OWL

17. …6/19/20112 10 WEB ONTOLOGY LANGUAGE (OWL)

19. It provides a rich collection of operators for forming concept descriptions

20. It is a W3C standard, promoting interoperation and sharing between applications

21. It has been designed to be compatible with existing web standards6/19/20112 11 WEB ONTOLOGY LANGUAGE (OWL)

22. The OWL language There are different syntactic forms of OWL: RDF’s XML-based syntax (primary syntax for OWL) an XML-based syntax that does not follow the RDF conventions (more easily read by human users) see http://www.w3.org/TR/owl-xmlsyntax/ an abstract syntax (used in the language specification document) (much more compact and readable) see http://www.w3.org/TR/owl-semantics/ a graphic syntax based on the conventions of UML (an easy way for people to become familiar with OWL) 6/19/20112 12 WEB ONTOLOGY LANGUAGE (OWL)

23. XML provides a surface syntax for structured documents, but imposes no semantic constraints on the meaning of these documents. XML Schema is a language for restricting the structure of XML documents and also extends XML with datatypes. RDF is a datamodel for objects ("resources") and relations between them, provides a simple semantics for this datamodel, and these datamodels can be represented in an XML syntax. RDF Schema is a vocabulary for describing properties and classes of RDF resources, with a semantics for generalization-hierarchies of such properties and classes. OWL adds more vocabulary for describing properties and classes: among others, relations between classes (e.g. disjointness), cardinality (e.g. "exactly one"), equality, richer typing of properties, characteristics of properties (e.g. symmetry), and enumerated classes. 6/19/20112 13 WEB ONTOLOGY LANGUAGE (OWL)

24. Header OWL documents are usually called OWL ontologies, and are RDF documents. So the root element of a OWL ontology is an rdf:RDF element which also species a number of namespaces. For example: <rdf:RDF xmlns:owl="http://www.w3.org/2002/07/owl#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf- syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:xsd="http://www.w3.org/2001/XLMSchema#"> 6/19/20112 14 WEB ONTOLOGY LANGUAGE (OWL)

25. An OWL ontology may start with a collection of assertions for housekeeping purposes. These assertions are grouped under an owl:Ontologyelement which contains comments, version control and inclusion of other ontologies. For example: <owl:Ontologyrdf:about=""> <rdfs:comment>An example OWL ontology</rdfs:comment> <owl:priorVersionrdf:resource="http://www.mydomain.org/uni-ns-old"/> <owl:importsrdf:resource="http://www.mydomain.org/persons"/> <rdfs:label>University Ontology</rdfs:label> </owl:Ontology> 6/19/20112 15 WEB ONTOLOGY LANGUAGE (OWL)

26. XML a meta language that allows you to create and format your own document markups a method for putting structured data into a text file; these files are - easy to read - unambiguous - extensible - platform-independent 6/19/20112 16 WEB ONTOLOGY LANGUAGE (OWL)

27. XML a family of technologies: - XML 1.0 - Xlink - Xpointer & Xfragments - CSS, XSL, XSLT - DOM - XML Namespaces - XML Schemas 6/19/20112 17 WEB ONTOLOGY LANGUAGE (OWL)

28. The pieces there are 3 components for XML content: - the XML document - DTD (Document Type Declaration) - XSL (Extensible Stylesheet Language) The DTD and XSL do not need to be present in all cases 6/19/20112 18 WEB ONTOLOGY LANGUAGE (OWL)

29. RDF Ontology Language? RDF stands for Resource Description Framework RDF is a framework for describing resources on the web RDF provides a model for data, and a syntax so that independent parties can exchange and use it RDF is designed to be read and understood by computers RDF is not designed for being displayed to people RDF is written in XML RDF is a part of the W3C's Semantic Web Activity RDF is a W3C Recommendation RDFS language features allow for modeling certain semantic aspects of a domain of interest 6/19/20112 19 WEB ONTOLOGY LANGUAGE (OWL)

30. RDF Schema (RDFS) is an extension to RDF. RDF Schema provides the framework to describe application-specific classes and properties Classes in RDF Schema is much like classes in object oriented programming languages. This allows resources to be defined as instances of classes, and subclasses of classes. 6/19/20112 20 WEB ONTOLOGY LANGUAGE (OWL)

31. RDFS Example <?xml version="1.0"?> <rdf:RDF xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xml:base= "http://www.animals.fake/animals#"> <rdf:Description rdf:ID="animal"> <rdf:typerdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> </rdf:Description> <rdf:Descriptionrdf:ID="horse"> <rdf:typerdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> <rdfs:subClassOfrdf:resource="#animal"/> </rdf:Description> </rdf:RDF> 6/19/20112 21 WEB ONTOLOGY LANGUAGE (OWL)

32. References Grigoris Antoniou1 and Frank van Harmelen2(pages 5 - 7) www.csc.liv.ac.uk/~frank/teaching/comp08/lecture6.pdf www.w3.org/TR/owl-features/ www.w3.org/2004/OWL/ www.csd.abdn.ac.uk/.../OWLTheWebOntologyLanguage/ static.twoday.net/71desa1bif/files/W3C-OWL-Overview.pdf (pages ) https://wiki.imise.uni-leipzig.de/Lehre/2005WS/SOntEng/files?get W3C Specification: http://www.w3.org/RDF/ 6/19/20112 22 WEB ONTOLOGY LANGUAGE (OWL)