Okech Odhiambo Faculty of Information Technology Strathmore University Semantic Web Technologies: The foundation for future enterprise systems Okech Odhiambo Faculty of Information Technology Strathmore University

Outline The Current Web and the Semantic Web RDF and RDF Schema Web Ontology Language OWL Application areas for semantic web technology Our reflections

Introduction In this talk we chose to look at the languages of the Semantic Web Specifically RDF, RDF Schema and OWL They are W3C recommendations We believe that as web developers, these languages are a necessary part of the skill set required of you Two most significant Next Big Thing concepts that will change the way IT is used are: The semantic applications Web services Microsoft in September Microsoft's recent reorganization and the increased emphasis on Internet technologies being developed in its MSN unit are reactions to the changing computing landscape enabler of Web services

The Current Web Content is designed for human consumption. Main focus is on documents a document or media can link to any other document (or different media). In the current web is content is designed for human consumption. The main focus is on documents. The universality is based on the concept that a document or media can link to any other document (or different media). the Syntactic Web A hypermedia, a digital library A library of documents called (web pages) interconnected by a hypermedia of links A database, an application platform A common portal to applications accessible through web pages, and presenting their results as web pages A platform for multimedia BBC Radio 4 anywhere in the world! Terminator 3 trailers! A naming scheme Unique identity for those documents A place where computers do the presentation (easy) and people do the linking and interpreting (hard). Why not get computers to do more of the hard work?

Scientific American, May 2001: An extension of the current web in which information is given a well defined meaning, better enabling computers and people to work in cooperation

The Layer ‘Cake’ View 2005 version Note: the lowest levels in the stack are ‘enabling technologies’ the middle layers are the core semantic web technologies the upper layers are still (logic, proof and trust) research issues. View 2005 version

Semantic Web Languages Resource Description Framework (RDF) RDF is a language ( + XML syntax + semantics) for representing metadata for describing the semantics of information in a machine- accessible way RDF Schema (RDFS) extends RDF with “schema vocabulary” Class, Property type, subClassOf, subPropertyOf range, domain RDFS is a very simple ontology language

The RDF Data Model Statements are (subject, predicate, object) triples: (fAcosta, hasWritten, “Research Methods in IT”) Can be represented as a graph: fAcosta hasWritten subject object predicate Research Methods in IT Statements describe properties of resources. A resource is any object that can be pointed to by a URI: Properties themselves are also resources (URIs)

Uniform Resource Identifier - URI "The generic set of all names/addresses that are short strings that refer to resources" URLs (Uniform Resource Locators) are a particular type of URI, used for resources that can be accessed on the WWW (e.g., web pages) In RDF, URIs typically look like “normal” URLs, often with fragment identifiers to point at specific parts of a document: http://www.somedomain.com/some/path/file#fragmentID Example: http://ks.strathmore.edu/example/#facosta Shorthand notation strath:facosta

“Problem Based Learning Methodology” Linking Statements The subject of one statement can be the object of another Such collections of statements form a directed, labeled graph http://ks.strathmore.edu/example/facosta “Freddie Acosta” http://ks.strathmore.edu/example/IT2145 “Problem Based Learning Methodology” mailto:facosta@strathmore.edu http://ks.strathmore.edu/example/Title http://ks.strathmore.edu/example/homePage http://www.strathmore.edu/lecturers/facosta http://ks.strathmore.edu/example/email http://ks.strathmore.edu/example/hasName http://ks.strathmore.edu/example/hasWritten

RDF Syntax RDF has an XML syntax Every Description element describes a resource Every attribute or nested element inside a Description is a property of that Resource <rdf:Description rdf:about="http://ks.strathmore.edu/example/facosta"> <homePage rdf:resource="http://www.strathmore.edu/lecturers/facosta"/> <hasName>Freddie Acosta</strath:hasName> <email rdf:resource="mailto:facosta@strathmore.edu"/> <hasWritten rdf:resource=“strath:IT2145"/> </rdf:Description> <rdf:Description rdf:about="http://ks.strathmore.edu/example/IT2145"> <Title>Problem Based Learning Methodology</Title>

RDF Schema RDF gives a language for meta data annotation, and a way to write it down in XML, but it does not provide any way to structure the annotations RDF Schema augments RDF to allow you to define vocabulary terms and the relations between those terms it gives “extra meaning” to particular RDF predicates and resources e.g., Class, subClassOf, Property, domain, range These terms are the RDF Schema building blocks (constructors) used to create vocabularies

strath:JournalArticle RDF Schema - Classes strath:Publication strath:IT2145 strath:JournalArticle strath:Article rdf:Type rdf:subClassOf rdfs:Class rdfs:Type rdfs:subClassOf This is a simple hierarchy of the publications in a university Class and property belongs to the class rdfs:resource

RDF Schema - Properties strath:Publication rdfs:subClassOf rdfs:Type strath:hasWritten rdfs:Property rdfs:Domain rdf:Range strath:Employee rdfs:Class strath:Faculty Problems with RDF Schema RDFS too weak to describe resources in sufficient detail No localised range and domain constraints Can’t say that the range of hasChild is person when applied to persons and elephant when applied to elephants No existence/cardinality constraints Can’t say that all instances of person have a mother that is also a person, or that persons have exactly 2 parents No transitive, inverse or symmetrical properties Can’t say that isPartOf is a transitive property, that hasPart is the inverse of isPartOf, or that touches is symmetrical Need to extend RDFS to provide better support for ontologies Difficult to provide reasoning support No “native” reasoners for non-standard semantics May be possible to reason via FO axiomatisation

Ontology Borrowed from philosophy - the study of “The nature of being” “An ontology is a formal, explicit specification of a shared conceptualization specification of a conceptualization” (Gruber, 1993) In general, an ontology provides a mechanism to capture information about the objects and the relationships that hold between them in some domain of interest.

An Ontology Language for the Semantic Web Create a richer ontology language for the Semantic Web Desirable features identified for Web Ontology Language: Extend existing Web standards Such as XML, RDF, RDFS Easy to understand and use Formally specified Possible to provide automated reasoning support Of “adequate” expressive power

OWL Overview OWL is an ontology language, based on ideas from Description Logics It has well defined semantics OWL extends the expressive power of RDFS Can talk about defined properties of classes Ontology Inference language – OIL DARPA Agent Markup Language – DAML Merged to DAMAL+OIL Web Ontology Working group WebONT recommended OWL –Feb 2004 Two languages were developed to satisfy above requirements OIL: developed by group of (largely) European researchers DAML-ONT: developed by group of (largely) US researchers Efforts merged to produce DAML+OIL Done by a “Joint EU/US Committee on Agent Markup Languages” DAML+OIL was submitted to W3C as basis for standardization Web-Ontology (WebOnt) Working Group developed OWL language based on DAML+OIL OWL language now a W3C Recommendation OWL RDF/RDFS XML Schema Description Logics

Components of an OWL Ontology Individuals Classes Properties Employee Publication Country Research Methods in IT Philippines Clement Acosta Advanced Accounting Kenya UK isCitizenOf hasColleague hasWritten

The Three Species of OWL OWL-Full - No restrictions on how/where language constructs can be used. The union of OWL and RDF Schema OWL-Full is not decidable. OWL-DL - Restricted version of OWL-Full. Corresponds to a description logic. Certain restrictions on how/where language constructs can be used in order to guarantee decidability. OWL-Lite - A subset of OWL-DL. The simplest and easiest to implement of the three species. Three species of OWL OWL full is union of OWL syntax and RDF OWL DL restricted to well-behaved fragment ( DAML+OIL) OWL Lite is “easier to implement” subset of OWL DL

SW Application Areas Application Areas … many more Knowledge Management Focus of our research group: Knowledge Systems group Enterprise Data Integration Web services, to support E-Commerce (B2C and B2B) Context based search E-Government E0learning … many more

Take Home Message The semantic web is here with us Be familiar with these technology Semantic Web technologies have a promising future and an exciting potential RDF and OWL are already standards no need to learn a proprietary languages Tools are available for semantic web applications. Common ones are Jena (http://jena.sourceforge.net/) is a Java framework for building Semantic Web applications Protégé (http://protege.stanford.edu) is an ontology editor and a knowledge-base editor. It has an OWL Plug-in now provides support for editing Semantic Web ontologies.

Questions?

Layer Cake - Revised W3C Semantic Web Language Layer Cake revised version, Tim-Berners-Lee 2005 Back to 2000 Version

Example OWL Ontology Consider a simple family ontology A Woman is a Person who is Female Parent is a Person having at least one child A Mother is a Female Parent. In DL Syntax Woman ≡ Person ∏ Female Parent ≡ Person ∏  (≥ 1 hasChild) • Person Mother ≡ Person ∏  (≥ 1 hasChild) • Person ∏ Female

OWL in RDF/XML Syntax (1) <owl:Class rdf:ID="Woman"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <owl:Class rdf:ID="Female"/> <owl:Class rdf:ID="Person"/> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> <owl:Class rdf:ID="Mother"> <owl:Class rdf:about="#Parent"/> <owl:Class rdf:about="#Woman"/>

OWL in RDF/XML Syntax (2) <owl:Class rdf:about="#Parent"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <owl:Restriction> <owl:onProperty> <owl:ObjectProperty rdf:ID="hasChild"/> </owl:onProperty> <owl:minCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#int" >1</owl:minCardinality> </owl:Restriction> <owl:Class rdf:about="#Person"/> </owl:intersectionOf> </owl:Class> </owl:equivalentClass>

Use Protégé instead for ontology development

OWL Classes OWL is an ontology language that is primarily designed to describe and define classes. Classes are therefore the basic building blocks of an OWL ontology. OWL supports six main ways of describing classes: Named Class, Intersection classes, Union classes, Complement classes, Restrictions, Enumerated classes.

OWL Properties There are two main categories of properties: Object properties and datatype properties. Object properties link individuals to individuals. Datatype properties link individuals to datatype values (e.g. integers, floats, strings).

Reasoning For ontologies that fall into the scope of OWL-DL, we can use a reasoner to infer information that isn’t explicitly represented in an ontology. Standard ‘reasoning services’ are: Subsumption testing Equivalence testing Consistency testing Instantiation testing