1. 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

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

3. 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

4. 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?

5. 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

6. 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

7. 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

8. 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)

9. 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:
Example:
Shorthand notation strath:facosta

10. “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
“Freddie Acosta”
“Problem Based Learning Methodology”

11. 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="
<homePage rdf:resource="
<hasName>Freddie Acosta</strath:hasName>
<
<hasWritten rdf:resource=“strath:IT2145"/>
</rdf:Description>
<rdf:Description rdf:about="
<Title>Problem Based Learning Methodology</Title>

12. 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

13. 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

14. 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

15. 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.

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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 ( is a Java framework for building Semantic Web applications
Protégé ( is an ontology editor and a knowledge-base editor. It has an OWL Plug-in now provides support for editing Semantic Web ontologies.

22. Questions?

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

24. 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

25. 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"/>

26. 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=" >1</owl:minCardinality>
</owl:Restriction>
<owl:Class rdf:about="#Person"/>
</owl:intersectionOf>
</owl:Class>
</owl:equivalentClass>

27. Use Protégé instead for ontology development

28. 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.

29. 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).

30. 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