Semantic Web

1
Semantic Web
http//www.srdc.metu.edu.tr/ibrahim/courses/cse53
7
2
Semantic Web Initiative

• Originally Tim Berners-Lee's attempt to answer
  the question What is the full potential of the
  (World Wide) Web?
• The semantic web is an extension of the current
  web in which information is given well-defined
  meaning, better enabling computers and people to
  work in cooperation
• T. Berners-Lee, J. Hendler, O. Lassila, The
  Semantic Web, Scientific American, May 2001.

3
Describing Metadata

• Metadata is structured data about data
• To fully exploit the opportunities brought by Web
  
• Metadata of the resources need to be made
  explicit to make it automatically processable
• Search engines or software agents can easily
  extract and aggregate information from different
  sites

4
Metadata vs Ontology

• A well-defined metadata description language
  enables to automatically process a description to
  extract its metadata
• However to interpret the metadata automatically
  through a program or a software agent its meaning
  (semantics) must also be known
• Meaning of data is given through domain specific
  ontologies

5
In short

• The semantic web is based on machine-processable
  semantics of data.
• Its backbone technology are Ontologies.
• It is based on new web languages such as XML,
  RDF, and OWL, and tools that make use of these
  languages.
• It repairs obvious problems of the current web.

6
Some History

• "I think there's a world market for about 5
  computers. Thomas J. Watson, Chairman of the
  Board, IBM (around 1948)
• There is no reason for any individuals to have a
  computer in their home.Ken Olsen, President,
  Chairman and Founder of DEC, 1977
• 640K ought to be enough for anybody. Bill
  Gates, 1981 (Bill Gates denies having ever said
  that)
• ... Until someone finds a way for applications
  to understand each other, the effect of Web
  services technology will be fairly limited. When
  I pass customer data across the Web in a
  certain format using a Web Services interface,
  the receiving program has to know what that
  format is. You have to agree on what the
  business objects look like. And no one has come
  up with a feasible way to work that out yet --
  not Oracle, and not its competitors...Oracle
  Chairman and CEO Larry Ellison, (around 2003)

7
Ontology
8
What is an Ontology?
An explicit formal specification of the terms in
the domain and relations among them. - Noy
and McGuinness, Ontology Development 101

• The word ontology comes from the Greek ontos
  (being) and logos (word)
• An ontology describes objects and concepts as
  classes
• These classes are arranged in a hierarchy, and
  then class attributes and relationships are
  described with properties

9
An Ontology Provides

• A common vocabulary An ontology describes
  consensual knowledge, that is, it describes
  meaning which has been accepted by a group not by
  a single individual
• Ability to define relationships among classes,
  properties and instances
• Automated Processing
• Querying
• Reasoning
• the enabling technology for the semantic web.

10
Ontology Languages

• RDF Resource Description Framework
• DAMLOIL Extends RDF with more sophisticated
  class and property definitions (by DARPA and
  On-To-Knowledge project (European Commission,
  IST-1999-10132))
• DAML Darpa Agent Markup Language
• OIL Ontology Inference Layer
• OWL Web Ontology Language by W3C
• (Based on DAMLOIL)
• DAML-S by DAML Services Coalition (for Web
  Services)
• OWL-S OWL for Web Services by W3C

11
RDF Resource Description Language
12
Resource Description Framework

• RDF is a W3C recommendation
• It provides syntax and schema to express meta
  data describing resources on the Web, enables
  meta data interoperability
• RDF Model and Syntax specification gives us
  recognisable metadata by defining the XML tags to
  express RDF constructs in XML.
• RDF Schemas gives us a mechanism for defining
  shared vocabularies. Unlike the tree/forest-type
  hierarchy model of XML documents, RDF-Schema
  models a directed graph which is more suitable
  for expressing relationships

13
RDF Schema

• Provides an XML vocabulary to
• express classes and their (subclass)
  relationships.
• define properties and associate them with
  classes.
• Facilitates
• inferencing on data, and
• enhanced searching.

14
An Simple RDF Description Example
lt?xml version 1.0?gt ltrdfRDF
xmlnsrdfhttp//www.w3.org/1999/rdf-syntax-ns
xmlnsshttp//description.org/schema/gt
ltrdf Description about http//www.TaxHeaven.c
om/ TaxPreparationServicegt
ltsPaymentMethodgt CreditCardlt/sPaymentMethodgt
lt/rdfDescriptiongt lt/rdfRDFgt
15
RDF Schema is about creating Taxonomies!
NaturallyOccurringWaterSource
BodyOfWater
Stream
Ocean
River
Tributary
Brook
Lake
Sea
Properties length Literal emptiesInto
BodyOfWater
Rivulet
16
What inferences can be made on this RDF/XML,
given the taxonomy on the last slide?
What inferences can be made with this data?
lt?xml version"1.0"?gt ltRiver rdfID"Yangtze"
xmlnsrdf"http//www.w3.org/1999/02/22-rd
f-syntax-ns" xmlns"http//www.geodes
y.org/water/naturally-occurring"gt
ltlengthgt6300 kilometerslt/lengthgt
ltemptiesInto rdfresource"http//www.china.org/ge
ographyEastChinaSea"/gt lt/Rivergt
Yangtze.rdf
Inferences are made by examining a taxonomy that
contains River. See next slide.
17
NaturallyOccurringWaterSource
BodyOfWater
Stream
Ocean
River
Tributary
Brook
Lake
Sea
Properties length Literal emptiesInto
BodyOfWater
Inference Engine
Rivulet
lt?xml version"1.0"?gt ltRiver rdfID"Yangtze"
xmlnsrdf"http//www.w3.org/1999/02/22-rd
f-syntax-ns" xmlns"http//www.geodes
y.org/water/naturally-occurring"gt
ltlengthgt6300 kilometerslt/lengthgt
ltemptiesInto rdfresource"http//www.china.org/ge
ographyEastChinaSea"/gt lt/Rivergt
Yangtze.rdf
Inferences - Yangtze is a Stream - Yangtze
is an NaturallyOcurringWaterSource -
http//www.china.org/geographyEastChinaSea is a
BodyOfWater
18
How does a taxonomy facilitate searching?
NaturallyOccurringWaterSource
BodyOfWater
Stream
Ocean
River
Tributary
Brook
Lake
Sea
Properties length Literal emptiesInto
BodyOfWater
Rivulet
The taxonomy shows that when searching for
"streams", any RDF/XML that uses the class Brook,
Rivulet, River, or Tributary are relevant. See
next slide.
19
NaturallyOccurringWaterSource
BodyOfWater
Stream
Ocean
River
Tributary
Brook
Lake
Sea
Properties length Literal emptiesInto
BodyOfWater
Search Engine
Rivulet
"Show me all documents that contain info about
Streams"
lt?xml version"1.0"?gt ltRiver rdfID"Yangtze"
xmlnsrdf"http//www.w3.org/1999/02/22-rd
f-syntax-ns" xmlns"http//www.geodes
y.org/water/naturally-occurring"gt
ltlengthgt6300 kilometerslt/lengthgt
ltemptiesInto rdfresource"http//www.china.org/ge
ographyEastChinaSea"/gt lt/Rivergt
Yangtze.rdf
Results - Yangtze is a Stream, so this
document is relevant to the query.
20
Everything about RDF Schemas!

• RDF Schemas is all about defining taxonomies
  (class hierarchies).
• As we've seen, a taxonomy can be used to make
  inferences and to facilitate searching.
• That's all there is to RDF Schemas!
• The rest is just syntax
• The previous slide showed the taxonomy in a
  graphical form. Obviously, we need to express
  the taxonomy in a form that is machine-processable
  . RDF Schemas provides an XML vocabulary to
  express taxonomies.

21
RDF Core Classes

• For convenience, namespace prefix rdf is used
  for RDF Syntax, rdfs for RDF Schemas.
• rdfsResource - All things being described by RDF
  expressions are resources and are considered to
  be instances of the top-level/root class
  rdfsResource
• rdfsClass - represents the generic concept of a
  type or category and can be defined to represent
  almost everything, e.g. Web pages, people,
  document types
• rdfProperty - represents the subset of RDF
  resources that are properties

22
RDF Core Properties

• rdfssubClassOf - This property specifies a
  subset / superset relation between classes
• rdfssubPropertyOf - is an instance of
  rdfProperty that is used to specify that one
  property is a specialization of another
• rdfs range - is used to define that the values
  of a property are instances of one or more stated
  classes
• rdfs domain - is used to state that any resource
  that has a given property is an instance of one
  or more classes

23
Example Classes and Subclass property
Resource
Person
Man
Woman

• ltrdfsClass rdfIDPerson "gt
• ltrdfssubClassOf
• rdfsresource"http//www.w3.org/rdfschemaRes
  ource"/gt
• lt/rdfsClassgt
• ltrdfsClass rdfIDWoman"gt
• ltrdfssubClassOf rdfsresourcePerson"/gt
• lt/rdfsClassgt

24
RDF Property Example
integer
Woman
Man

• ltrdfProperty rdfIDhasAge"gt
• ltrdfsdomain rdfresourceWoman"/gt
• ltrdfsrange rdfresourcexsdInteger"/gt
• lt/rdfPropertygt
• ltrdfProperty rdfIDhasHusband"gt
• ltrdfsdomain rdfresourceWoman"/gt
• ltrdfsrange rdfresourceMan"/gt
• lt/rdfPropertygt

25
An Example Class Instance in RDF
35
Susan
Robert

• ltWoman rdfIDSusan"gt
• lthasAgegt35lt/hasAgegt
• lthasHusband resourceRobert/gt
• lt/Womangt
• ltMan rdfIDRobert/gt

26
An Example RDF definition
lt?xml version"1.0" encoding"UTF-8" ?gt ltrdfRDF
xmlnsrdf"http//www.w3.org/TR/WD-rdf-syntax"
xmlnsrds"http//www.w3.org/TR
/WD-rdf-schema"
xmlnsMESChain"http//www.srdc.metu.edu.tr/sc/com
mon.schema.rdf"gt ltrdfDescription
ID"Product"gt ltrdftype resource"http//www.w
3.org/TR/WD-rdf-schemaClass"/gt
ltrdssubClassOf resource"http//www.w3.org/TR/WD-
rdf-schemaResource"/gt ltrdslabelgtProductlt/rds
labelgt ltrdscommentgtAll kinds of trade
Productslt/rdscommentgt lt/rdfDescriptiongt
ltrdfDescription ID"Sub_Part_Required"gt
ltrdftype resource"http//www.w3.org/TR/WD-rdf-sy
ntaxProperty"/gt ltrdslabelgtSub Part
Oflt/rdslabelgt ltrdsdomain resource"Product"/
gt ltrdsrange resource"Product"/gt
ltrdscommentgtCritical sub components of an
aggregated productlt/rdscommentgt
lt/rdfDescriptiongt lt/rdfRDFgt
27
An Example RDF definition - Contd
ltrdfDescription ID"computer"gt ltrdftype
resource"http//www.w3.org/TR/WD-rdf-schemaClass
"/gt ltrdssubClassOf resource"Product"/gt
ltMESChainAdded_Value resource"printer"/gt
ltMESChainAdded_Value resource"scanner"/gt
ltMESChainSub_Part_Required resource"main.board"/
gt ltMESChainSub_Part_Optional
resource"hard.disk"/gt ltMESChainSub_Part_O
ptional resource"cdrom"/gt
ltMESChainSub_Part_Optional resource"mouse"/gt
ltrdslabelgtComputerlt/rdslabelgt
ltrdscommentgtAll kinds of Computerslt/rdscommentgt
lt/rdfDescriptiongt
28
Dublin Core

• dublincore.org
• One of the first usages of RDF in real life
• Dublin Core is an initiative to provide
  standardized (thus interoperable) resource
  descriptions on the Web
• Internationally recognised model for metadata for
  resource discovery
• Basis of most developments elsewhere
• 16 core elements

29
Core Elements in Dublin Core

• Title Creator Subject
• Description Publisher Contributor
• Date Type Format
• Identifier Language Relation
• Source Coverage Rights

30
A Sample Definition using DC
ltrdfDescription about"http//www.srdc.metu.edu.
tr/sc/D2/D2.catalog.xml"gt ltdcTitlegtD2's
Electronic Cataloglt/dcTitlegt
ltdcSubjectgtDistributorlt/dcSubjectgt
ltdcTypegtElectronic_Cataloglt/dcTypegt
ltdcFormatgtCBL 1.2 - catalog.dtdlt/dcFormatgt
ltdcIdentifiergt"www.srdc.metu.edu.tr/sc/D2/D2.cata
log.rdf"lt/dcIdentifiergt ltdcDategt1999-02-02lt/
dcDategt ltdcCreatorgtDistributor
D2lt/dcCreatorgt ltdcPublishergtDistributor
D2lt/dcPublishergt ltdcDescriptiongtThis
resource contains the electronic catalog of
distributor D2 in XML conforming to CBL 1.2
lt/dcDescriptiongt lt/rdfDescriptiongt
31
Advantages of RDF

• RDF fixes the syntax and structure of describing
  metadata through RDF Syntax
• It allows meaning to be defined and associated
  with data through RDF Schema
• RDF Schema facilities defining domain specific
  ontologies

32
Limitations of RDF

• Although you can express a lot with RDF Schemas,
  it lacks some very desirable expressiveness, such
  as
• Two classes, same concept - people use different
  words to represent the same thing. It would be
  very useful to be able to state "this class is
  equivalent to this second class".
• One person may create an ontology with a class
  called "Airplane". Another person may create an
  ontology with a class called "Plane". It would
  be useful to be able to indicate that the two
  classes are equivalent.
• Cardinality constraints - often it is necessary
  to indicate the allowable number of occurrences
  of a property
• Ex We would like to be able to express that a
  person has only and only "one" age.

33
RDF Schemas Building Block to More Expressive
Ontology Languages
34
RDF Schema vs XML Schema

• XML Schemas is all about syntax.
• RDF Schema is all about semantics.
• An XML Schema tool is intended to validate that
  an XML instance conforms to the syntax specified
  by the XML Schema.
• An RDF Schema tool is intended to provide
  additional facts to supplement the facts in
  RDF/XML instances.
• XML Schemas is prescriptive - an XML Schema
  prescribes what an element may contain, and the
  order the child elements may occur.
• RDF Schemas is descriptive - an RDF Schema simply
  describes classes and properties.

35
RDF Some References

• RDF Schema Resource Description Framework Schema
  Specification, W3C Proposed Recommendation, 1999,
  http//www.w3.org/TR/PR-rdf-schema.
• RDF Syntax Resource Description Framework Model
  and Syntax Specification,W3C Recommendation,
  1999, http//www.w3.org/TR/REC-rdf-syntax
• Costello, R. L., Jacobs, D.B., Inferring and
  Discovering Relationships using RDF Schemas,
  lsdis.cs.uga.edu/cartic/reading/rdf_inference/
  rdfs.ppt
• The Dublin Core Metadata Initiative,
  http//dublincore.org/

36
Web Ontology Language OWL
37
OWL RDF Schema more

• All of the elements/attributes provided by RDF
  and RDF Schema can be used when creating an OWL
  document
• OWL classes permit much greater expressiveness
  than RDF Schema classes
• Consequently, OWL has created its own Class,
  owlClass

38
RDF Schema Features used in OWL

• rdfsClass
• rdfProperty
• rdfssubClassOf
• rdfssubPropertyOf
• rdfsdomain
• rdfsrange

39
Defining Property Characteristics

• RDF Schema provides three ways to characterize a
  property
• range use this to indicate the range of values
  for a property.
• domain use this to associate a property with a
  class.
• subPropertyOf use this to specialize a property
• OWL documents also use rdfsrange, rdfsdomain,
  and rdfssubPropertyOf
• OWL has many more property types that are useful
  in inferencing!

40
Ontology Languages and OWL
OIL Ontology Inference Layer (European
Commission Project)
DAMLDarpa Agent Markup Language
DAMLOIL
RDF (Resource Description Framework)
OWL Web Ontology Language (Being Standardized
by W3C)
41
OWL provides three decreasingly expressive
sublanguages

• OWL Full is meant for users who want maximum
  expressiveness with no computational guarantees
• It is unlikely that any reasoning software will
  be able to support complete reasoning for OWL
  Full
• OWL DL supports those users who want the maximum
  expressiveness while retaining computational
  completeness (all conclusions are guaranteed to
  be computable) and decidability (all computations
  will finish in finite time)
• OWL Lite supports those users primarily needing a
  classification hierarchy and simple constraints

42
OWL Lite Features

• (In)Equality
• equivalentClass
• equivalentProperty
• sameAs
• differentFrom
• AllDifferent
• distinctMembers
• Property Characteristics
• ObjectProperty
• DatatypeProperty
• inverseOf
• TransitiveProperty
• SymmetricProperty
• FunctionalProperty
• InverseFunctionalProperty

43
OWL Lite Features

• Property Type Restrictions
• Restriction
• onProperty
• allValuesFrom
• someValuesFrom
• Class Intersection
• intersectionOf

44
OWL Full Language constructs that are in addition
to those of OWL Lite

• Class Axioms
• oneOf, dataRange
• disjointWith
• equivalentClass(applied to class expressions)
• rdfssubClassOf(applied to class expressions)

• Boolean Combinations of Class Expressions
• unionOf
• intersectionOf
• complementOf
• Arbitrary Cardinality
• minCardinality
• maxCardinality
• cardinality
• Filler Information
• hasValue

45
OWL Classes

• Ministry of Interior has defined ontologies for
  their information in OWL
• For example

ltowlClass rdfIDCrimes"gt lt/owlClassgt
ltowlClass rdfIDRobbery"gt
ltrdfssubClassOf rdfresource"Crimes"/gt lt/owlCl
assgt

ltowlClass rdfIDTerrorism"gt
ltrdfssubClassOf rdfresource"Crimes"/gt lt/owlCl
assgt
46
OWL Properties
description

• ltowlDatatypeProperty rdfIDdescription"gt
• ltrdfsdomain rdfresource"Crime"/gt
• ltrdfsrange rdfresourcehttp//www.w3
• .org/2001/XMLSchemaLiteral"/gt
  
• lt/owlDatatypeProperty gt
• ltowlObjectProperty rdfIDsuspect"gt
• ltrdfsdomain rdfresource"Robbery"/gt
• ltrdfsrange rdfresourceThiefgt
• lt/owlObjectProperty gt
• ltowlObjectProperty rdfIDdriver"gt
• ltrdfsdomain rdfresource"Speeding"/gt
• ltrdfsrange rdfresourceSpeeder"/gt
• lt/owlObjectProperty gt

driver
47
An Example (From Ref 3)

• Finger prints from a robbery scene identified
  John Smith as the suspect
• Here is the police report on the robbery

ltRobbery rdfID"report-2004-07-27-xyz"gt
ltdescriptiongt...lt/descriptiongt ltsuspectgt
ltThief rdfabout"http//www.ministryOfInterior.go
v/criminalsJohn_Smith"/gt lt/suspectgt lt/Robberygt
48
An Example (Continued)

• Later in the day a police gives a person a
  ticket for speeding
• The driver's license showed the name John Doe
• Here is the police report on the speeder

ltSpeeding rdfID"report-2004-07-27-abc"gt
ltdescriptiongt...lt/descriptiongt ltdrivergt
ltSpeeder rdfabout"http//www.ministryOfInterio
r/criminalsJohn_Doe"/gt lt/drivergt lt/Speedinggt
49
Any Relationship between the Thief and the
Speeder?
Ministry of Interior keeps the OWL descriptions
of their files
ltCriminals rdfabout" http//www.ministryOfInter
ior/criminalsJohn_Doe "gt ltowlsameAs
rdfresource" http//www.ministryOfInterior.gov/
criminalsJohn_Smith "/gt lt/Criminalsgt
50
An Example OWL Reasoning (Continued)
Inference The Thief and the Speeder are one and
the same!

• OWL provides a property (owlsameAs) for
  indicating that two resources (e.g., two people)
  are the same

51
Multiple Inheritance

• ltowlClass rdfIDSpeeder"gt
• ltrdfssubClassOf rdfresource"Criminals"
  /gt
• ltrdfssubClassOf rdfresourcePerson/gt
• lt/owlClassgt

Criminals
Person
Speeder
52
Enumeration

• A class description of the "enumeration" kind is
  defined with the owloneOf property
• The value of this built-in OWL property must be a
  list of individuals that are the instances of the
  class
• This enables a class to be described by
  exhaustively enumerating its instances
• ltowlClass rdfID"ProductAvailability"/gt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfIDInStock"/gt
• lt owlThing rdfIDOutOfStock"/gt
• lt owlThing rdfIDSpecialOrder"/gt
• lt/owloneOfgt
• lt/owlClassgt

53
Boolean Combination of Class Expressions

• ltowlClass rdfabout"Person"gt
• ltowlunionOf rdfparseType"owlCollection"gt
• ltowlClass rdfabout"Man"/gt
• ltowlClass rdfabout"Woman"/gt
• lt/owlunionOfgt
• lt/owlClassgt

54
Boolean Combination of Class Expressions

• ltowlClass rdfabout"PrerequisiteCourses"gt
• ltowlintersectionOf rdfparseType"Collection"gt
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Ceng351" /gt
• ltowlThing rdfabout"Ceng352" /gt
• lt/owloneOfgt lt/owlClassgt
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Ceng351" /gt
• ltowlThing rdfabout"Ceng520" /gt
• lt/owloneOfgt lt/owlClassgt lt/owlintersectionO
  fgt
• lt/owlClassgt

55
Boolean Combination of Class Expressions

• ltowlClass rdfID"Car"gt
• ltrdfscommentgtno car is a personlt/rdfscommentgt
• ltrdfssubClassOfgt
• ltowlClassgt
• ltowlcomplementOf rdfresource"Person"/gt
• lt/owlClassgt
• lt/rdfssubClassOfgt
• lt/owlClassgt
• ltowlClass rdfIDVegetablesgt
• ltowlcomplementOfgt
• ltowlClass rdfresource"Meat"/gt
• lt/owlcomplementOfgt
• lt/owlClassgt

56
Class Axioms

• ltowlClass rdfIDSpeeder"gt
• ltrdfssubClassOf rdfresource"Criminals"
  /gt
• ltrdfssubClassOf rdfresourcePerson/gt
• ltowldisjointWith rdfresourceTerrorists/
  gt
• lt/owlClassgt
• ltowlClass rdfIDGraduateCourses"gt
• ltowlequivalentClassgt
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltCourse rdfabout"Ceng520"/gt
• ltCourse rdfabout"Ceng532"/gt
• ltCourse rdfabout"Ceng540"/gt
• lt/owloneOfgt lt/owlClassgt lt/owlequivalentClassgt
  
• lt/owlClassgt

57
Property Restrictions

• ltowlClass rdfID"Person"gt
• ltrdfssubClassOfgt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasPare
  nt"/gt
• ltowlallValuesFrom rdfresource"Pers
  on"/gt
• lt/owlRestrictiongt lt/rdfssubClassOfgt
  lt/owlClassgt
• All values of the property are members of the
  class extension
• owlallValuesFrom constraint demands that all
  values of property P should be of type T.

58
Property Restrictions

• The following example defines a class of
  individuals who have at least one parent who is a
  physician
• ltowlClass rdfIDDoctorChildren"gt
• ltrdfssubClassOf rdfresourcePersongt
• ltrdfssubClassOfgt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasParent"/gt
  
• ltowlsomeValuesFrom rdfresource"Phys
  ician"/gt
• lt/owlRestrictiongt
• lt/rdfssubClassOfgt
• lt/owlClassgt

59
Property Restrictions

• The following example describes the class of
  individuals who have the individual referred to
  as Bush as their parent
• ltowlClass rdfIDBushChildren"gt
• ltrdfssubClassOf rdfresourcePersongt
• ltrdfssubClassOfgt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasParent"/gt
  
• ltowlhasValue rdfresource"Bush"/gt
• lt/owlRestrictiongt
• lt/rdfssubClassOfgt
• lt/owlClassgt

60
Property Restrictions

• ltowlClass rdfID"Person"gt
• ltrdfssubClassOfgt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasPare
  nt"/gt
• ltowlallValuesFrom rdfresource"Pers
  on"/gt
• lt/owlRestrictiongt
• lt/rdfssubClassOfgt
• ltrdfssubClassOfgt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasParent"/gt
• ltowlminCardinality rdfdatatype"xsdnonNegati
  veInteger"gt 0 lt/owlminCardinalitygt
• ltowlmaxCardinality rdfdatatype"xsdnonNegati
  veInteger"gt 2 lt/owlmaxCardinalitygt
• lt/owlRestrictiongt
• lt/rdfssubClassOfgt
• lt/owlClassgt

61
owlinverseOf

• Relating properties
• Self explanatory!
• ltowlObjectProperty rdfID"hasChild"gt
• ltowlinverseOf rdfresource"hasParent"/gt
• lt/owlObjectPropertygt
• If A is parent of B, then B is child of A.

62
Global Cardinality Constraints on Properties

• owlFunctionalProperty For each instance there
  is at most one value for the property
• ltowlFunctionalProperty rdfID"hasAge"gt
• ltrdfsdomain rdfresource"Person" /gt
• ltrdfsrange rdfresource"xsdnonNegativeIntege
  r" /gt
• lt/owlFunctionalPropertygt
• There can only be one age of a person (at a
  given time)
• Note that many people may have the same age!

63
Global Cardinality Constraints on Properties

• owlInverseFunctionalPropertyThe object of a
  property statement uniquely determines the
  subject
• ltowlInverseFunctionalProperty
  rdfID"biologicalMotherOf"gt ltrdfsdomain
  rdfresource"Woman"/gt
• ltrdfsrange rdfresource"Human"/gt
  lt/owlInverseFunctionalPropertygt
• There can only be one biological mother of a
  human being
• Note that a mother can have several children!

64
Logical Characteristics of Properties

• Self explanatory!
• ltowlSymmetricProperty rdfID"friendOf"gt
• ltrdfsdomain rdfresource"Human"/gt
• ltrdfsrange rdfresource"Human"/gt
• lt/owlSymmetricPropertygt
• If person A is a friend of person B, then
  (consequently) person B is a friend of person A.

65
Logical Characteristics of Properties

• When a property P is defined as transitive
  property, this means that
• if a pair (x,y) is an instance of P, and
• the pair (y,z) is also instance of P, then
• we can infer the the pair (x,z) is also an
  instance of P
• ltowlTransitiveProperty rdfID"subRegionOf"gt
• ltrdfsdomain rdfresource"Region"/gt
• ltrdfsrange rdfresource"Region"/gt
• lt/owlTransitivePropertygt
• Or it can equivalently be written as
• ltowlObjectProperty rdfID"subRegionOf"gt
• ltrdftype rdfresource"owlTransitiveProperty"/
  gt
• ltrdfsdomain rdfresource"Region"/gt
• ltrdfsrange rdfresource"Region"/gt
• lt/owlObjectPropertygt

66
An Example
Since subRegionOf is a transitive property, from
this information an OWL reasoner should be able
to derive that Izmir is a sub region of Turkey

ltowlClass rdfIDRegion"gt lt/owlClassgt
ltRegion rdfIDTurkey/gt
ltRegion rdfIDEgegt lt subRegionOf
rdfresource"Turkey"/gt lt/Regiongt
ltRegion rdfIDIzmirgt lt subRegionOf
rdfresource"Ege"/gt lt/Regiongt
67
Individual Identity

• The built-in OWL owldifferentFrom property links
  an individual to an individual
• An owldifferentFrom statement indicates that two
  URI references refer to different individuals
• ltowlClass rdfabout"Person"gt
• lt/owlClassgt
• ltPerson rdfIDBill_Clintongt
• ltowldifferentFrom rdfresourceW_Bush/gt
• lt/Persongt

68
Individual Identity

• For ontologies in which the unique-names
  assumption holds, the use of owldifferentFrom is
  likely to lead to a large number of statements,
  as all individuals have to be declared pairwise
  disjoint
• For such situations OWL provides a special idiom
  in the form of the construct owlAllDifferent
• owlAllDifferent is a special built-in OWL
  class, for which the property owldistinctMembers
  is defined, which links an instance of
  owlAllDifferent to a list of individuals
• ltowlAllDifferentgt
• ltowldistinctMembers rdfparseType"Collection"gt
  
• ltPerson rdfabout"Bill_Clinton"/gt
• ltPerson rdfabout"W_Bush"/gt
• ltPerson rdfabout"A_Lincoln"/gt
  lt/owldistinctMembersgt
• lt/owlAllDifferentgt

69
OWL Summary

• OWL is an Ontology Specification Language
• It is build on RDF with DAMLOIL experience
• OWL has more expressive power than RDF such as
• Boolean Combinations of Class Expressions
  (unionOf, intersectionOf, complementOf, )
• Several Types of Properties (Transitive,
  Functional, Symmetric, )
• Equivalence or disjointness of classes

70
OWL References (I)

• OWL Web Ontology Language Reference
  http//www.w3.org/TR/owl-ref/
• Costello, R. L., Jacobs, D. B., OWL Web Ontology
  Language, www.racai.ro/EUROLAN-2003/html/presentat
  ions/JamesHendler/owl/OWL.ppt
• Costello, R. L., Jacobs, D. B., A Quick
  Introduction to OWL Web Ontology Language,
  www.daml.org/meetings/2003/05/SWMU/briefings/
  08_Tutorial_D.ppt

71
OWL References (II)

• Antoniou, G., Harmalen, F., Web Ontology
  Language OWL, in Handbook on Ontologies,
  Springer, 2004
• Horrocks, I., DAMLOIL A Description Logic for
  the Semantic Web, IEEE Data Engineering
  Bulletin, Vol. 25, No. 1, March 2000
• McGuinness, D., Harmelen, F.,OWL Web Ontology
  Language Overview, http//www.w3.org/TR/owl-featur
  es/
• Smith, M., Welty, C., McGuinnes, D., OWL Web
  Ontology Language Guide, http//www.w3.org/TR/owl-
  guide/

72
Semantic Web Services
73
General Vision - 1
74
The General Vision - 2

• Serious Problems in information
• finding
• extracting
• representing
• interpreting
• and maintaining

WWW
URI, HTML, HTTP
Static
75
The General Vision - 3
76
The General Vision - 4
77
Remember that...

• Web Services are self-contained, self-describing,
  modular applications that can be published,
  located, and invoked across the Web
• Dynamic service invocation is possible through
• Web Services Description Language (WSDL)
• Simple Object Access Protocol (SOAP)

78
Triangle Architecture for Web Services
79
WS as Programming Technology
80
Main Limitation of Web Services

• Web Services are promising
• They can be accessed and executed over the web
• However
• Service descriptions (in UDDI) are based on
  structurednatural language descriptions.
• WSDL is syntactical in nature and provides only
  technical information
• Therefore
• Human programmer needs to be kept in the loop
• Scalability and economy of web services are a
  concern

81
Semantic Web Services

• Semantic Web Services combine Semantic Web and
  Web Service Technology.
• Automatization of Web Service Discovery,
  Combination and Invocation makes the technology
  scalable.
• This combination opens the way to make web
  service technology scalable and mature.
• SWS is a pre-requisite to enable fully open,
  flexible, and dynamic eWork and eCommerce a
  reality.

82
Semantic Web Services

• Self-contained, self-describing, semantically
  marked-up software resources that can be
  published, discovered, composed and executed
  across the Web in a task driven automatic way
  Arroyo et al. 2004

83
Semantic Web Services

• In order to exploit services in their full
  potential their properties must be defined such
  as
• The methods of charging and payment
• The channels by which the service is requested
  and provided
• Constraints on temporal and spatial aspects
• Availability
• Service quality
• Security, trust and rights attached to a service
• This in turn is possible only by describing the
  semantics of Web services through ontology
  languages

84
WSDL does not describe Web service semantics
Semantic description of the properties of a
service in DAML-S
Web Service Description
defines
uses
Web Service
Service Consumer
85
Taxonomies are not enough to define service
semanticsAn Example Taxonomy UNSPSC
43.00.00.00.00 Communications and
Computer Equipment and Peripherals and Components
and Supplies
43.16.17.00.00 Business Transaction and
Personal Business Software
43.16.17.02.00 Tax Preparation Software
86
An Example Ontology for Travel Domain
TravelService
Entertainment Service
Accommodation Service
Transportation Service
AirTransportation
ReserveAFlight
BuyATicket
87
Properties of ReserveAFlight Generic Service
How to relate MyService to a generic service
class?
MyService
88
Ontology Languages

• Have formal specification that enables querying
• Provide the means to define sophisticated class
  properties
• Therefore, DAML and OWL are extended for Web
  Services
• DAML-S by DAML Services Coalition (for Web
  Services)
• OWL-S OWL for Web Services by W3C

89
DAML-S SemanticWebService Model
describedByHow it works
90
DAML-S ServiceProfile Class

• Some of the properties of ServiceProfile class
  are
• parameter property
• For example, a subproperty is input, another
  output
• serviceParameters, subproperties of which may be
  max response time, geographicRadius,
• serviceType, high level classification of service
  such as B2B or B2C
• serviceCategory, refers to an ontology of
  services, it is necessary to define domain
  specific ontologies
• And more

91
Questions