The document provides an overview of semantic web standards and technologies, emphasizing the challenges of current web information retrieval and the vision for a more machine-processable web. Key technologies discussed include RDF, ontologies, and logic, which aim to enhance data sharing and processing across applications. The document also addresses RDF syntax, RDF Schema (RDFS), and how they enable the description of resources and classifications within the semantic web framework.

1. State of the Art in
Semantic Web standards
and technologies
Andreas Duscher

2. State of the Art in
Semantic Web Standards
and Technologies
 General Overview
 RDF / RDF Schema
 OWL
 OWL-S
 Final words

3. Today´s web
 It is designed for human consumption
 Information retrieval is mainly supported by keyword-based
search engines
 Some problems with information retrieval:
 High recall, low precision
 Low or no recall
 Results are highly sensitive to vocabulary
 Web content is not machine-proccessable
„I am a professor of computer science.“
-- or --
„I am a professor of computer science, you may
think. Well….“

4. Semantic Web Vision
„The Semantic Web provides a common framework that
allows data to be shared and reused across application,
enterprise, and community boundaries.“
[http://www.w3.org/2001/sw/]
Problem „Business-to-consumer
electronic commerce“
• Manually retrieving the best offers from
different online-shops is too time-consuming.
• Tools for shoping are available in the form of
shop bots.
• For every online shop a wrapper is needed
(information is extracted through text analysis).
Vision „Business-to-consumer
electronic commerce“
• The user asks a autonomously acting piece
of software for a certain product.
• The software retrieves all offers and
compares them with the user‘s preferences.
• If needed the sofware negotiates with the
shop for a special discount or tries to get a
trusted rating for the shop.

5. Semantic Web Technologies
 Ontologies
 An ontology describes formally a domain of
discourse.
 It is a finite list of terms and the relationship
between these terms.
 Types of relationship: subclass hierarchy,
properties, value restrictions, logical relationships
between objects
 „In the context of web an ontology provide a
shared understanding of a domain.“

6. Semantic Web Technologies
 Logic
 „A discipline that studies the principles of reasoning.“
 Automated reasoners allow to draw conclusions from
given knowledge, make implicit knowledge explicit.
prof(X) -> faculty(X)
faculty(X) -> staff(X)
prof(michael)

7. Semantic Web Technologies
 Logic
 „A discipline that studies the principles of reasoning.“
 Automated reasoners allow to draw conclusions from
given knowledge, make implicit knowledge explicit.
prof(X) -> faculty(X)
faculty(X) -> staff(X)
prof(michael)
faculty(michael)
staff(michael)
prof(X) -> staff(X)
This example involves knowledge typically found in
ontologies.

8. Semantic Web Technologies
 Agents
 Agents are pieces of software that work autonomously
and proactively.
 A personal agent would recieive some task and
preferences from the user, communicate with other
agents, compare information and select certain
choices.
 Web services
 collection of protocols and standard for exchanging
data between various applications

9. Semantic Web Technologies
 How it fits together?
 Onotologies can be used to represent knowledge, interpret
the retrieved information and communicate with other
agents.
 Logic can be used for processing the retrieved information
and for drawing conclusions.
 Agent / Web service technologies allow the communication
between different systems and the composition of
complexer services from simple ones.

10. Semantic Web Technologies
 How it fits together?
 Onotologies can be used to represent knowledge, interpret
the retrieved information and communicate with other
agents.
=> RDF / RDF Schema / OWL
 Logic can be used for processing the retrieved information
and for drawing conclusions.
=> Defining an OWL-based language is in progress!
 Agent / Web service technologies allow the communication
between different systems and the composition of
complexer services from simpler ones.
=> OWL-S

11. RDF Motivation
 The Resource Description Framework (RDF) is a
language for representing resources in the World Wide
Web.
 RDF is intended for situations in which this information
needs to be processed by applications, rather than being
only displayed to people.
 RDF is based on the idea of identifying things using Web
identifiers (URIs).

12. RDF Basic Concepts
 the thing the statement describes (the web page`s URL)
 a specific property of the thing (e.g. creator)
 the concrete message the statement wants to give,
in other words the value of the property (John Smith)
RDF basic ideas
 Things being described have properties, which have values
 Resources can be described by making statements
(similar to the above example)
http://www.example.org/index.html has a creator whose value is John Smith
Example
„Imagine trying to state that someone named John Smith created a particular
Web page.“

13. RDF Basic Concepts
RDF terminology
 the part that identifies the thing the statemant is about is called subject
 the part that identifies the property is called predicate
 the part that identifies the value of the property is called object
Subject Object
Predicate

14. RDF Basic Concepts
RDF terminology
 the part that identifies the thing the statemant is about is called subject
 the part that identifies the property is called predicate
 the part that identifies the value of the property is called object
Subject Object
Predicate
http://www.example.org/index.html has a creator whose value is John Smith
 the subject is the URL „http://www.example.org/index.html“
 the predicate is the word „creator“
 the object is the name „John Smith“

15. RDF Basic Concepts
To make these statements machine-proccessable
two things are needed:
 a system of machine-processable identifiers (for subjects, predicates
and objects) without any possibilty of confusion between similar looking
identifiers

16. RDF Basic Concepts
To make these statements machine-proccessable
two things are needed:
 a system of machine-processable identifiers (for subjects, predicates
and objects) without any possibilty of confusion between similar looking
identifiers
 a machine-processable language for representing these statements and
exchanging them between machines

17. RDF Basic Concepts
To make these statements machine-proccessable
two things are needed:
 a system of machine-processable identifiers (for subjects, predicates
and objects) without any possibilty of confusion between similar looking
identifiers
 a machine-processable language for representing these statements and
exchanging them between machines
Uniform Resource Identifiers (URI) allow to identify and uniquely
name things - even if they have no network-accessible location.

18. RDF Basic Concepts
To make these statements machine-proccessable
two things are needed:
 a system of machine-processable identifiers (for subjects, predicates
and objects) without any possibilty of confusion between similar looking
identifiers
 a machine-processable language for representing these statements and
exchanging them between machines
RDF defines a XML markup language, named RDF/XML, which
allows to represent RDF statements.
Uniform Resource Identifiers (URI) allow to identify and uniquely
name things - even if they have no network-accessible location.

19. RDF Model
As mentioned:
 RDF makes statements about resources
 Each statement consists of a subject, a predicate and an object
http://www.example.org/index.html has a creator whose value is John Smith
http://www.example.org/staffid/5232
http://purl.org/dc/elements/1.1/creator
http://www.example.org/index.html

20. RDF Model
As mentioned:
 RDF makes statements about resources
 Each statement consists of a subject, a predicate and an object
http://www.example.org/index.html has a creator whose value is John Smith
http://www.example.org/staffid/5232
http://purl.org/dc/elements/1.1/creator
http://www.example.org/index.html
subject
object
predicate

21. RDF Model
Conclusion
 RDF documents are „nodes-and-arcs diagrams
interpreted as statements about things identified
by URIrefs“.
 So subjects, predicates and objects can be
identified by URIrefs.

22. RDF Syntax
http://www.example.org/terms/creation-date
http://www.example.org/index.html
August 16, 1999
<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:exterms="http://www.example.org/terms/">
<rdf:Description rdf:about="http://www.example.org/index.html">
<exterms:creation-date>August 16, 1999</exterms:creation-
date>
</rdf:Description>
</rdf:RDF>

23. RDF Syntax
http://www.example.org/terms/creation-date
August 16, 1999
<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:exterms="http://www.example.org/terms/">
<rdf:Description rdf:about="http://www.example.org/index.html">
<exterms:creation-date>August 16, 1999</exterms:creation-date>
<dc:creator rdf:resource="http://www.example.org/staffid/85740"/>
</rdf:Description>
</rdf:RDF>
http://www.example.org/staffid/4252
http://www.example.org/index.html
http://purl.org/dc/elements/1.1/creator

24. RDF Syntax
Abbreviating and Organizing RDF URIrefs
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#
xmlns:exterms="http://www.example.com/terms/">
<rdf:Description rdf:ID="item10245">
<exterms:model rdf:datatype="&xsd;string">Overnighter</exterms:model>
<exterms:sleeps rdf:datatype="&xsd;integer">2</exterms:sleeps>
<exterms:weight rdf:datatype="&xsd;decimal">2.4</exterms:weight>
<exterms:packedSize rdf:datatype="&xsd;integer">784</exterms:packedSize>
</rdf:Description>
 rdf:about and rdf:ID are strictly speaking the same.
rdf:about is often used for talking about resources that have been defined
elsewhere.
 The value of rdf:ID can only appear once in a document.
 The fragment identifier item10245 will be interpreted relative to a base URI.

25. RDF Syntax
Typing in RDF
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#
xmlns:exterms="http://www.example.com/terms/">
<rdf:Description rdf:ID="item10245">
<rdf:type rdf:resource="http://www.example.com/terms/Tent"/>
<exterms:model rdf:datatype="&xsd;string">Overnighter</exterms:model>
<exterms:sleeps rdf:datatype="&xsd;integer">2</exterms:sleeps>
…
</rdf:Description>
 RDF allows to classify resources with the special attribute rdf:type.
 The resource item10245 is called a tpyed node.
 It is similar to the programming language concept of objects and classes
=> RDF Schema (RDFS)

26. RDF Syntax
Typing in RDF (abbreviated form)
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#
xmlns:exterms="http://www.example.com/terms/">
<exterms:Tent rdf:ID="item10245">
<exterms:model rdf:datatype="&xsd;string">Overnighter</exterms:model>
<exterms:sleeps rdf:datatype="&xsd;integer">2</exterms:sleeps>
…
</exterms:Tent>
 RDF allows to classify resources with the special attribute rdf:type.
 The resource item10245 is called a tpyed node.
 It is similar to the programming language concept of objects and classes
=> RDF Schema (RDFS)

27. RDFS Basics
 What it is not
 RDF Schema does not make any assumptions about any
application domain, nor does it define the semantics.
 What it is
 RDF Schema provides a vocabulary to describe classes of
things and/or resources.
 Vocabulary descriptions written in RDF Schema language
are legal RDF graphs.
It is up to the user to devolpe a RDF Schema (RDFS) for
the needed application domain.

28. RDFS Basics
 Own namespace http://www.w3.org/2000/01/rdf-schema#
 Core classes
 rdfs:Resource, the class of all resouces
 rdfs:Class, the class of all classes
 rdf:Property, the class of all properties
Properties can be used to characterize concrete classes
In RDF Schema, a class is any resource having an rdf:type
property whose value is the resource rdfs:Class.

29. RDFS Basics
 Core properties
 rdf:type, relates a resource to its class
So the resource is an instance of the class
 rdfs:subClassOf, relates a class to one of its superclasses
 rdfs:subPropertyOf, relates a property to one of its superproperties
The above properties are instances of the class
rdf:Property. Own properties can be defined by assigning
the type rdf:Property to any kind of resource.

30. RDFS Example (Classes)
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<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://example.org/schemas/vehicles">
<rdf:Description rdf:ID="MotorVehicle">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-chema#Class"/>
</rdf:Description>
<rdf:Description rdf:ID="PassengerVehicle">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdf:Description>
<rdf:Description rdf:ID="Truck">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdf:Description>
<rdf:Description rdf:ID="Van">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdf:Description>
<rdf:Description rdf:ID="MiniVan">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#Van"/>
<rdfs:subClassOf rdf:resource="#PassengerVehicle"/>
</rdf:Description>
</rdf:RDF>

31. RDFS Example (Classes)
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<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://example.org/schemas/vehicles">
<rdf:Description rdf:ID="MotorVehicle">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-chema#Class"/>
</rdf:Description>
<rdf:Description rdf:ID="PassengerVehicle">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdf:Description>
<rdf:Description rdf:ID="Truck">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdf:Description>
<rdf:Description rdf:ID="Van">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdf:Description>
<rdf:Description rdf:ID="MiniVan">
<rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
<rdfs:subClassOf rdf:resource="#Van"/>
<rdfs:subClassOf rdf:resource="#PassengerVehicle"/>
</rdf:Description>
</rdf:RDF>
resource with an unique id
property „rdf:type“
that defines this
resource as „Class“
property „rfds:subClassOf“ with
a resource as value, in this
case a formerly defined class

32. RDFS Example (Classes)
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<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://example.org/schemas/vehicles">
<rdfs:Class rdf:ID="MotorVehicle"/>
<rdfs:Class rdf:ID="PassengerVehicle">
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdfs:Class>
<rdfs:Class rdf:ID="Truck">
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdfs:Class>
<rdfs:Class rdf:ID="Van">
<rdfs:subClassOf rdf:resource="#MotorVehicle"/>
</rdfs:Class>
<rdfs:Class rdf:ID="MiniVan">
<rdfs:subClassOf rdf:resource="#Van"/>
<rdfs:subClassOf rdf:resource="#PassengerVehicle"/>
</rdfs:Class>
</rdf:RDF>
Abbreviated form
The value of the
property „rdf:type“
can be used for
naming the whole
resource.

33. RDFS Example (Properties)
<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<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://example.org/schemas/vehicles">
…
<rdf:Property rdf:ID="registeredTo">
<rdfs:domain rdf:resource="#MotorVehicle"/>
<rdfs:range rdf:resource="#Person"/>
</rdf:Property>
<rdf:Property rdf:ID="rearSeatLegRoom">
<rdfs:domain rdf:resource="#PassengerVehicle"/>
<rdfs:range rdf:resource="&xsd;integer"/>
</rdf:Property>
<rdfs:Class rdf:ID="Person"/>
</rdf:RDF>
„rdfs:range“ indicates,
that the values of that
property are instances of a
certain class
„rdfs:domain“ indicates,
that the values of the
particular property applies
to a designated class

34. RDFS Example (Instances)
<?xml version="1.0"?> <!DOCTYPE rdf:RDF [<!ENTITY xsd
"http://www.w3.org/2001/XMLSchema#">]>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:ex="http://example.org/schemas/vehicles#"
xml:base="http://example.org/things">
<ex:PassengerVehicle rdf:ID="johnSmithsCar">
<ex:registeredTo rdf:resource="http://www.example.org/staffid/85740"/>
<ex:rearSeatLegRoom rdf:datatype="&xsd;integer">
127
</ex:rearSeatLegRoom>
</ex:PassengerVehicle>
</rdf:RDF>
an instance of the class
„PassengerVehicle“
the defined properties that
can be applied to this class

35. RDF / RDFS Conclusion
 Expressivity of RDF and RDF Schema is limited
 Local scope of properties
 Disjointness of classes
 Boolean combination of classes
 Cardiniality restrictions
 Special characteristics of properties
 Need for standardized ontology language
that builds upon existing concepts of RDF / RDFS
=> OWL Web Ontology Language

36. OWL Hierarchy
rdfs:Resource
rdfs:Class rdf:Property
owl:Class owl:ObjectProperty owl:DatatypeProperty

37. OWL Syntax
 Class elements
 Classes are defined using owl:Class
<owl:Class rdf:ID=“associateProfessor“>
<rdfs:subClassOf rdf:resource=“#academicStaffMember“ />
</owl:Class>
 Disjoint classes
<owl:Class rdf:about=“#associateProfessor“>
<owl:disjointWith rdf:resource=“#professor“ />
<owl:disjointWith rdf:resource=“#assistantprofessor“ />
</owl:Class>
 Equivalence of classes
<owl:Class rdf:ID=“faculty“>
<owl:equivalentClass rdf:resource=“#academicStaffMember“/>
</owl:Class>

38. OWL Syntax
 Property elements
 Datatype properties relate objects to datatype values
<owl:DatatypeProperty rdf:ID=“age“>
<rdfs:range rdf:resource=“http://www.w3.org/2001/XMLSchema
#nonNegativeInteger“ />
</owl:Class>
 Object properties relate objects to other objects
<owl:ObjectProperty rdf:ID=“isTaughtBy“>
<rdfs:domain rdf:resource=“#course“/>
<rdfs:range rdf:resource=“#academicStaffMember“/>
</owl:Class>
<owl:ObjectProperty rdf:ID=“teaches“>
<rdfs:domain rdf:resource=“#academicStaffMember“/>
<rdfs:range rdf:resource=“#course“/>
<owl:inverseOf rdf:resource=“#isTaughtBy“/>
</owl:Class>

39. OWL Syntax
 Property restrictions
Allow to specify constraints on classes and properties
<owl:Class about:ID=“#firstYearCourse“>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource=“#isTaughtBy“/>
<owl:allValuesFrom rdf:resource=“#Professor“/>
</owl:Restriction>
</rdfs:subClassOf>
</owl:Class>
<owl:Class about:ID=“#course“>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource=“#isTaughtBy“/>
<owl:minCardinality
rdf:datatype=“#&xsd;nonNegativeInteger“/>
</owl:Restriction>
</rdfs:subClassOf>
</owl:Class>

40. Web Services and the
Semantic Web
 The Semantic Web should enable users to
locate, select, employ, compose, and monitor
Web-based services automatically.
 Computer-interpretable description of the
service is needed.
 OWL-S defines an ontology for describing
web services.

41. Web Services and the
Semantic Web
 What does the service
provide?
ServiceProfile
A profile is used for advertizing the
service.
 How is it used?
ServiceModel
A model describes how a service
works.
 How to interact with it?
ServiceGrounding
A grounding provides the needed
details about transport protocols.

42. Web Services and the
Semantic Web (ServiceProfile)
<owl:Class rdf:ID="Profile">
<rdfs:label>Profile</rdfs:label>
<rdfs:subClassOf rdf:resource="&service;#ServiceProfile" />
<rdfs:comment> Definition of Profile </rdfs:comment>
</owl:Class>
<owl:ObjectProperty rdf:ID="hasInput">
<rdfs:subPropertyOf rdf:resource="#hasParameter"/>
<rdfs:range rdf:resource="&process;#Input"/>
</owl:ObjectProperty>

43. Web Services and the
Semantic Web (ServiceModel)

44. Web Services and the
Semantic Web (ServiceModel)
<owl:Class rdf:ID="SimpleProcess">
<rdfs:subClassOf rdf:resource="#Process"/>
<owl:disjointWith
rdf:resource="#AtomicProcess"/>
</owl:Class>
<owl:ObjectProperty rdf:ID="realizedBy">
<rdfs:domain rdf:resource="#SimpleProcess"/>
<rdfs:range rdf:resource="#AtomicProcess"/>
<owl:inverseOf rdf:resource="#realizes"/>
</owl:ObjectProperty>
<owl:ObjectProperty rdf:ID="realizes">
<rdfs:domain rdf:resource="#AtomicProcess"/>
<rdfs:range rdf:resource="#SimpleProcess"/>
<owl:inverseOf rdf:resource="#realizedBy"/>
</owl:ObjectProperty>

45. Conclusion
 Today‘s web and its problems
 A vision for a possible semantic web application
 Overview of important standards
 RDF / RDF Schema
 OWL
 OWL-S
The basic technologies exist but
- standards have to mature and
- more practical problems have to be solved
(tool support, ontology matching, …)

46. Bibliography
 D. Martin et al., „OWL-S Semantic Markup for Web Services“
http://www.daml.org/services/owl-s/1.1/overview/
 F. Manola and E. Miller, eds. „RDF Primer“, February 10, 2004.
http://www.w3.org/TR/rdf-primer/
 M. Smith et al., „OWL Web Ontology Language Guide“,
http://www.w3.org/TR/owl-guide/
 G. Antoniou, F. van Harmelen, „A Semantic Web Primer“, MIT
Press, London, England, 2004.