An Introduction to the

1

• An Introduction to the
• Semantic Web
• Part 1 XML, RDF and RDFS
• Jyotishman Pathak , AI Lab, Iowa State University
• jpathak_at_cs.iastate.edu_at_cs.iastate.edu

2
Outline

• Introduction Motivation
• XML
• RDF RDFS
• DL
• OWL
• Future Look Resources

3
World Wide Web

• WWW
• A global network that allows us to find, share,
  and combine information
• A web of links
• Information is represented using
• Natural Language (e.g., English)
• Graphics, Multimedia..
• O.K. for humans to comprehend
• Difficult for machine processing
• Ambiguity, Unconstrained data formats..

4
Example Searching

• Current search engines keywords
• Sensitive to syntax
• Insensitive to semantics
• High recall, low precision
• Query How many cows are there in Iowa?

1,234,567
5
Example Data Integration

• Databases are different in terms of structure,
  content
• Applications require managing several databases
• After company mergers (e.g., K-Mart Sears)
• Biochemical, Genetics etc..
• Semantics of the data(base) need to be specified
  explicitly (e.g., price cost)

6
What is required ?

• Ability for a resource to provide information
  about itself
• Better known as metadata
• E.g., Price refers to price of an item without
  taxes
• Ability to represent/store this information in
  machine-interpretable format
• Ability to design vocabularies which would give
  well-defined meaning to the information
• E.g., Price means the same as Cost
• Ability for agents to be able to reason about the
  (meta)data
• E.g., if B brother of A, C brother of B gt C
  brother of A
• The solution Semantic Web

7
The Semantic Web

• A global network in which information is given
  well-defined meaning, better enabling computers
  and people to work in cooperation
• Existing WWW is very human-oriented (E.g.,
  Google)
• A metadata based infrastructure for reasoning on
  the Web
• Herbivorous animals eat grass, Cow is
  herbivorous..
• Extends the current web, doesnt replace it..!

8
Semantic Web Layer Cake
9
Outline

• Introduction Motivation
• XML
• RDF RDFS
• DL
• OWL
• Future Look Resources

10
Road Map
We are here
11
XML

• A text-based meta-language format for data
  exchange
• Provides a pathway to transfer data easily
  between various applications
• Markup or Tags identifies structures in the
  document (ltnamegt lt/namegt)
• XML Schema provides a schema to XML files
• XML Query a typed query language for XML
  documents

12
An Example
ltbodygt ltpgtMichael Jackson has homepage lta
href"http//www.michaeljackson.com"gt http//www.m
ichaeljackson.comlt/agt and is the artist of
album lta href"http//www.music.org/songs/mj/Bad"gt
Badlt/agtlt/pgt lt/bodygt
Michael Jackson has a homepage http//www.michaelj
ackson.com and is the artist of album Bad
ltartistgt ltnamegtMichael Jacksonlt/namegt lthomepagegt
http//www.michaeljackson.comlt/homepagegt ltalbumgtB
adlt/albumgtlt/artistgt
13
XML file a labeled tree
ltartistgt ltnamegtlt/namegt lthomepagegtlt/homepagegt
ltalbumgtlt/albumgtlt/artistgt
Structure or Syntax
artist
name
album
homepage
14
Can XML provide Semantics ?

• ltPredatorgtlt/Predatorgt
• An un-manned aerial vehicle used by USAF for
  reconnaissance
• An organism that lives by preying on other
  organisms
• A company which specializes in manufacturing
  camouflage attire
• A movie by the current Governor of California

15
Limitations of XML

• Makes no commitment towards domain-specific
  vocabulary
• Interoperability (of meaning) feasible only for
  closed collaboration
• agents in a small stable community
• pages on a small stable intranet
• Not suitable for sharing information in WWW

16
Outline

• Introduction Motivation
• XML
• RDF RDFS
• DL
• OWL
• Future Look Resources

17
Road Map
We are here
18
What is Resource Description Framework ?

• Defines a framework for structuring describing
  resources (e.g., documents) in the Semantic Web
• Enables the definition of vocabularies for the
  description of the resources
• Goals
• Improved support for interpretation of data by
  machines
• Extensibility, interoperability, and reuse of
  vocabularies

19
The RDF Data Model

• Simple but powerful model for creation of
  metadata
• Can be expressed in XML
• Consists of three concepts
• Resource an element, a URI, a literal..
• Properties directed relations between two
  resources
• Statements triples of two resources bound by a
  property
• Usual terminology (s, p, o) subject, predicate,
  object

20
RDF Statement Graph

• Each triple (s, p, o) represents a RDF statement
• Michael Jackson is the artist of Bad

subject (resource)
predicate (property)
object (resource or literal)
http//www.music.org/songs/mj/Bad
http//www.michaeljackson.com
Artist
21
RDF Resource

• The Resource forms the central concept in RDF
• Anything can be described as a resource (E.g.,
  website, book, picture, persons..)
• Resources are identified by URIs (plus the
  optional anchor IDs)

http//www.music.org/songs/mj/Bad
http//www.michaeljackson.com
22
RDF Property

• Represents the predicate of an RDF statement
• Is labeled with a URI referencing to a RDF
  property
• Is directed pointing from the subject of a
  statement to the object of a statement

http//www.music.org/songs/mj/Bad
http//www.michaeljackson.com
Artist
musicArtist
23
Representing RDF documents

• RDF Graph Syntax (abstract syntax)
• Notation 3 and N-Triples
• XML Syntax
• XML Serialization Syntax
• Abbreviated XML Syntax Variations

24
An Example

• A person whose name is Michael Jackson and whose
  homepage is http//www.michaeljackson.com is the
  artist of http//www.music.org/songs/mj/Bad

25
How does RDF help?

• Vast majority of data processed by machines can
  be represented in the form of triples
• Subject, Predicate, Object are identified by
  URIs
• Allows to uniquely identify them
• Concepts are not just words in a document, but
  are tied to a unique definition found in the Web
• Uniqueness is vital to make a consistent
  statement
• Michael Jackson denoted by http//www.michaeljacks
  on.com means the same to everyone !

26
Why is RDF not enough?

• RDF properties can be regarded as attributes of
  resources
• RDF properties also represent relationships
  between resources
• But, RDF does not provide mechanisms for
  describing
• The properties (in terms of their range and
  domain)
• The relationships between the properties and
  other resources

27
Road Map
We are here
28
RDF(S) RDF Schema

• The RDF Vocabulary Description Language
• Enables us to
• Define classes of resources
• Define relationships between the classes
• Define the kinds of properties that instances of
  that classes have
• Define relationships between properties

29
ltrdfDescription IDModernMusic"gt ltrdftype
resource"http//www.w3.org/...Class"/gt
ltrdfssubClassOf rdfresource"http//www.w3.org/.
..Resource"/gt lt/rdfDescriptiongt ltrdfDescriptio
n ID"PopMusic"gt ltrdftype resource"http//ww
w.w3.org/...Class"/gt ltrdfssubClassOf
rdfresource"ModernMusic"/gt lt/rdfDescriptiongt
ltrdfDescription ID"Artist"gt ltrdftype
resource"http//www.w3.org/...Property"/gt
ltrdfsdomain rdfresource"PopMusic"/gt
ltrdfsrange rdfresource"Person"/gt lt/rdfDescrip
tiongt ltrdfDescription IDhasHomepage"gt
ltrdftype resource"http//www.w3.org/...Property
"/gt ltrdfssubPropertyOf rdfresource"Artist"
/gt lt/rdfDescriptiongt
30

• An Introduction to the
• Semantic Web
• Part 2 Description Logic and Web Ontology
  Language (OWL)
• Jie Bao, AI Lab, Iowa State University
• Baojie_at_cs.iastate.edu

31
Outline

• Introduction Motivation
• XML RDF
• RDFS
• OWL
• DL
• Future look and Resources

32
Map
You are here
33
Problems with RDFS

• RDFS too weak to describe resources in sufficient
  detail
• No localised range and domain constraints
• Cant say that the range of hasChild is person
  when applied to persons and elephant when applied
  to elephants
• No existence/cardinality constraints
• Cant say that all instances of Album have an
  artist that is also a person, or that albums have
  at least 1 artist
• No transitive, inverse or symmetrical properties
• Cant say that isPartOf is a transitive property,
  that hasPart is the inverse of isPartOf or that
  touches is symmetrical
• Difficult to provide reasoning support
• No native reasoners for non-standard semantics
• May be possible to reason via FO axiomatisation

34
Problems with RDFS

• RDFS is also too liberal
• No distinction between classes and instances
  (individuals)
• ltSpecies,type,Classgt
• ltLion,type,Speciesgt
• ltLeo,type,Liongt
• Properties can themselves have properties
• lthasDaughter,type,familyPropertygt
• No distinction between language constructors and
  ontology vocabulary, so constructors can be
  applied to themselves/each other
• lttype,range,Classgt
• ltProperty,type,Classgt
• lttype,subPropertyOf,subClassOfgt

35
Here comes the ontology

• The Tao that can be known is not Tao. The
  substance of the World is only a name for Tao. -
  Laozi, Tao Te Ching
• Science of Being (Aristotle, Metaphysics, IV, 1)

36
Ontology in Computer Science

• An ontology is an engineering artifact
• It is constituted by a specific vocabulary used
  to describe a certain reality, plus
• a set of explicit assumptions regarding the
  intended meaning of the vocabulary.
• Thus, an ontology describes a formal
  specification of a certain domain
• Shared understanding of a domain of interest
• Formal and machine manipulable model of a domain
  of interest
• An explicit specification of a
  conceptualisation Gruber93

37
Web Ontology Language Requirements

• Desirable features identified for Web Ontology
  Language
• Extends existing Web standards
• Such as XML, RDF, RDFS
• Easy to understand and use
• Should be based on familiar KR idioms
• Formally specified
• Of adequate expressive power
• Possible to provide automated reasoning support

38
Web Ontology Languages

• OIL (Ontology Interface Layer)
• Outcome from On-To-Knowledge project sponsored
  by European IST (Information Society
  Technologies) project
• DAML (DARPA Agent Markup Language)
• Began as a DARPA research program
• DAML-ONT
• DAMLOIL
• DAML combines OIL components
• DAML-S, DAML-L
• OWL (Web Ontology Language)
• W3C standard
• Future SWRL,

39
Evolution of Web Ontology Languages
1992 1998 1999
2000
2001 2002 2003
Combine vocabularies
OIL
Define vocabularies
Revision
XML
Extend vocabularies
RDFS
OWL
RDF
DAML (DAMLOIL)
DAML-ONT
SGML
For Web services
OWL-S
Extend HTML tags for semantic description
DAML-S
HTML
SHOE
40
OWL

• Three species of OWL
• OWL full is union of OWL syntax and RDF
• OWL DL restricted to FOL fragment (¼ DAMLOIL)
• OWL Lite is easier to implement subset of OWL
  DL
• Semantic layering
• OWL DL ¼ OWL full within DL fragment
• DL semantics officially definitive
• OWL DL based on SHIQ Description Logic
• In fact it is equivalent to SHOIN(Dn) DL
• OWL DL Benefits from many years of DL research
• Well defined semantics
• Formal properties well understood (complexity,
  decidability)
• Known reasoning algorithms
• Implemented systems (highly optimised)

41
OWL Language Constructs

• OWL Classes
• Class descriptions
• Enumeration
• Property restrictionValue constraints ,
  Cardinality constraints
• Intersection, union and complement
• Class axioms
• OWL Properties
• RDF Schema property constructs
• Relations to other properties
• Global cardinality restrictions on properties
• Logical characteristics of properties
• OWL Individuals
• Individual identity
• Datatypes
• Annotations

42
OWL Class Descriptions

• Enumeration
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Eurasia"/gt
• ltowlThing rdfabout"Africa"/gt
• ltowlThing rdfabout"NorthAmerica"/gt
• ltowlThing rdfabout"SouthAmerica"/gt
• ltowlThing rdfabout"Australia"/gt
• ltowlThing rdfabout"Antarctica"/gt
• lt/owloneOfgt
• lt/owlClassgt

43
OWL Class Descriptions

• Property Restriction
• Value constraints
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasAlbum" /gt
• ltowlallValuesFrom rdfresource"Album" /gt
• lt/owlRestrictiongt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasAlbum " /gt
• ltowlsomeValuesFrom rdfresource"BestSeller"
  /gt
• lt/owlRestrictiongt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasAlbum " /gt
• ltowlhasValue rdfresource"Bad" /gt
• lt/owlRestrictiongt

44
OWL Class Descriptions

• Property Restriction
• Cardinality constraints
• ltowlRestrictiongt
• ltowlonProperty rdfresource" hasAlbum" /gt
• ltowlmaxCardinalitygt2lt/owlmaxCardinalitygt
• lt/owlRestrictiongt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasAlbum " /gt
• ltowlminCardinalitygt2lt/owlminCardinalitygt
• lt/owlRestrictiongt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasAlbum " /gt
• ltowlcardinalitygt2lt/owlcardinalitygt
• lt/owlRestrictiongt

45
OWL Class Descriptions

• Intersection
• ltowlClassgt
• ltowlintersectionOf rdfparseType"Collection"
  gt
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Rock" /gt
• ltowlThing rdfabout"HeavyMetal" /gt
• lt/owloneOfgt
• lt/owlClassgt
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Rap" /gt
• ltowlThing rdfabout"Blues" /gt
• lt/owloneOfgt
• lt/owlClassgt
• lt/owlintersectionOfgt
• lt/owlClassgt

46
OWL Class Descriptions

• Union
• ltowlClassgt
• ltowlunionOf rdfparseType"Collection"gt
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Rock" /gt
• ltowlThing rdfabout"HeavyMetal" /gt
• lt/owloneOfgt
• lt/owlClassgt
• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Rap" /gt
• ltowlThing rdfabout"Blues" /gt
• lt/owloneOfgt
• lt/owlClassgt
• lt/owlunionOfgt
• lt/owlClassgt

47
OWL Class Descriptions

• Complement
• ltowlClass rdfIDNonStargt
• ltowlcomplementOfgt
• ltowlClass rdfabout"Star"/gt
• lt/owlcomplementOfgt
• lt/owlClassgt

48
OWL Class

• Subclass
• ltowlClass rdfIDRock"gt
• ltrdfssubClassOf rdfresource"Music" /gt
• lt/owlClassgt
• Equivalent Class
• ltowlClass rdfabout"US_President"gt
• ltowlequivalentClass rdfresource"PrincipalRes
  identOfWhiteHouse"/gt
• lt/owlClassgt
• Disjoint
• ltowlClass rdfabout"Man"gt
• ltowldisjointWith rdfresource"Woman"/gt
• lt/owlClassgt

49
OWL (RDFS) Properties

• RDF Schema Property Constructs
• ltowlObjectProperty rdfID" hasAlbum"gt
• ltrdfssubPropertyOf rdfresource"hasWork"/gt
• lt/owlObjectPropertygt
• Domain and Range
• ltowlSymmetricProperty rdfIDhasAlbum"gt
• ltrdfsdomain rdfresource"Artist"/gt
• ltrdfsrange rdfresource"Album"/gt
• lt/owlSymmetricPropertygt

50
OWL Properties

• Relations to Other Properties
• Equivalent property
• ltowlObjectProperty rdfIDhasAlbum"gt
• ltowlequivalentProperty rdfresource"hasCD"/gt
• lt/owlObjectPropertygt
• Inverse
• ltowlObjectProperty rdfIDhasAlbum"gt
• ltowlinverseOf rdfresource"hasArtist"/gt
• lt/owlObjectPropertygt

51
OWL Properties

• Global cardinality constraints on properties
• Functional property
• ltowlFunctionalProperty rdfIDhasName"gt
• ltrdfsdomain rdfresource"Person" /gt
• ltrdfsrange rdfresource"XMLSchemastring" /gt
• lt/owlFunctionalPropertygt
• Inverse functional property
• ltowlInverseFunctionalProperty
  rdfID"biologicalMotherOf"gt
• ltrdfsdomain rdfresource"Woman"/gt
• ltrdfsrange rdfresource"Human"/gt
• lt/owlInverseFunctionalPropertygt

52
OWL Properties

• Logical characteristics of properties
• Transitive property
• ltowlTransitiveProperty rdfID"subRegionOf"gt
• ltrdfsdomain rdfresource"Region"/gt
• ltrdfsrange rdfresource"Region"/gt
• lt/owlTransitivePropertygt
• Symmetric property
• ltowlSymmetricProperty rdfIDhasSameArtist"gt
• ltrdfsdomain rdfresource"Album"/gt
• ltrdfsrange rdfresource" Album"/gt
• lt/owlSymmetricPropertygt

53
OWL Individual

• Same as
• ltowlClass rdfIDMJ"gt
• ltowlsameAs rdfresource"http//www.michaeljacks
  on.com"/gt
• lt/owlClassgt
• Different from
• ltOpera rdfIDMJ"gt
• ltowldifferentFrom rdfresource"Madonna"/gt
• lt/Operagt
• All different
• ltowlAllDifferentgt
• ltowldistinctMembers rdfparseType"Collection"gt
• ltOpera rdfabout" Madonna "/gt
• ltOpera rdfabout" MJ"/gt
• ltOpera rdfabout"BritneySpears "/gt
• lt/owldistinctMembersgt
• lt/owlAllDifferentgt

54
Datatypes

• OWL uses RDF datatyping scheme
• Referencing XML Schema datatypes
• xsdinteger, xsddecimal, xsddouble, xsdstring,
  xsdboolean, xsdnonNegativeInteger,
  xsdnegativeInteger, xsddate,
• Enumerated datatype
• Using Datarange construct
• Datatype reasoning
• As a minimum xsdstring and xsdinteger
• For unsupported datatypes
• Lexically identical literals equal
• Lexically different literals would not be known
  to be either equal or unequal

55
Annotations

• Ontology header
• rdfslabel
• rdfscomment
• rdfsseeAlso
• rdfsisDefinedBy
• owlimports
• Version information
• owlversionInfo
• owlpriorVersion
• owlbackwardCompatibleWith
• owlincompatibleWith
• owlDeprecatedClass and owlDeprecatedProperty

56
Syntax RDF/XML
But XML is only an option. OWL could be
independent to XML
57
Syntax N-Triple

• lthttp//a.com/ontologyAlbumgt ltrdftypegt
  ltowlClassgt .
• lthttp//a.com/ontologyhasAlbumgt ltrdfsrangegt
  lthttp//a.com/ontologyAlbumgt .
• lthttp//a.com/ontologyMJgt lthttp//a.com/ontology
  hasNamegt "Michael Jackson"lthttp//www.w3.org/200
  1/XMLSchemastringgt .
• lthttp//a.com/ontologyhasNamegt ltrdfsdomaingt
  lthttp//a.com/ontologyPersongt .
• lthttp//a.com/ontologyBadgt ltrdftypegt
  lthttp//a.com/ontologyAlbumgt .
• lthttp//a.com/ontologyhasNamegt ltrdftypegt
  ltowlDatatypePropertygt .
• _A8b489fX3aX10092fc6cf9X3aXX2dX7fea
  ltowlunionOfgt ltrdfnilgt .
• lthttp//a.com/ontologyArtistgt ltrdftypegt
  ltowlClassgt .
• lthttp//a.com/ontologyArtistgt ltrdfssubClassOfgt
  lthttp//a.com/ontologyPersongt .
• _A8b489fX3aX10092fc6cf9X3aXX2dX7fea ltrdftypegt
  ltowlClassgt .
• lthttp//a.com/ontologyPersongt ltrdftypegt
  ltowlClassgt .
• lthttp//a.com/ontologyhasAlbumgt ltrdftypegt
  ltowlObjectPropertygt .
• lthttp//a.com/ontologyhasNamegt ltrdfsrangegt
  lthttp//www.w3.org/2001/XMLSchemastringgt .
• lthttp//a.com/ontologyMJgt ltrdftypegt
  lthttp//a.com/ontologyArtistgt .
• lthttp//a.com/ontologygt ltrdftypegt ltowlOntologygt
  .
• lthttp//a.com/ontologyhasAlbumgt ltrdfsdomaingt
  lthttp//a.com/ontologyArtistgt .

58
Outline

• Introduction Motivation
• XML RDF
• RDFS
• OWL
• DL
• Future look and Resources

59
Map
You are here
60
Why Logic

• Inference, Inference, Inference
• OWL can be used for inference
• MJ is a RockMusic artist, so he is also a
  PopMusic artist.
• But how?
• With a formal representation that equalvalent to
  OWL, but more easy to do inference.
• Its logic

61
Why Description Logic?

• Formal semantics (typically model theoretic)
• Decidable fragments of FOL
• Closely related to Propositional Modal Dynamic
  Logics
• Provision of inference services
• Sound and complete decision procedures for key
  problems
• Implemented systems (highly optimised)

62
DL Architecture
Knowledge Base
Tbox (schema)
CD Album u Music GoodArtist Artist u 9
gt10hasAlbum CD u
Interface
Inference System
Abox (data)
MJ Artist hMJ, Badi hasAlbum
63
Description Logic Family

• DLs are a family of logic based KR formalisms
• Particular languages mainly characterised by
• Set of constructors for building complex concepts
  and roles from simpler ones
• Set of axioms for asserting facts about concepts,
  roles and individuals
• ALC is the smallest DL that is propositionally
  closed
• Constructors include booleans (and, or, not), and
• Restrictions on role successors

64
DL Concept and Role Constructors

• Range of other constructors found in DLs,
  including
• Number restrictions (cardinality constraints) on
  roles, e.g., gt3 hasChild, 1 hasMother
• Qualified number restrictions, e.g., gt2
  hasChild.Female, 1 hasParent.Male
• Nominals (singleton concepts), e.g., Italy
• Concrete domains (datatypes), e.g.,
  hasAge.(gt21), earns
  spends.lt
• Inverse roles, e.g., hasChild- (hasParent)
• Transitive roles, e.g., hasChild (descendant)

65
DL Knowledge Base

• DL Knowledge Base (KB) normally separated into 2
  parts
• TBox is a set of axioms describing structure of
  domain (i.e., a conceptual schema), e.g.
• HappyFather ? Man ?hasChild.Female
• Elephant lt Animal Large Grey
• transitive(ancestor)
• ABox is a set of axioms describing a concrete
  situation (data), e.g.
• JohnHappyFather
• ltJohn,MarygthasChild
• Separation has no logical significance
• But may be conceptually and implementationally
  convenient

66
OWL as DL Class Constructors
67
OWL as DL Axioms
68
OWL DL Semantics

• Mapping OWL to equivalent DL (SHOIN(Dn))
• Facilitates provision of reasoning services
  (using DL systems)
• Provides well defined semantics
• DL semantics defined by interpretations I (DI,
  I), where
• DI is the domain (a non-empty set)
• I is an interpretation function that maps
• Concept (class) name A ! subset AI of DI
• Role (property) name R ! binary relation RI over
  DI
• Individual name i ! iI element of DI

69
What the hell SHOIN(Dn) is

• S ALCR
• ALC
• R transitive property
• H Role hierarchy
• O Nominal
• I Inverse role
• N unqualified number restriction, eg
• Dn n-ary datatype predicate.

70
DL Semantics
71
Interpretation Example
AI

• ? v, w, x, y, z
• AI v, w, x
• BI x, y
• RI (v, w), (v, x), (y, x), (x, z)
• B v,w,z
• A u B x
• A t B y
• 9 R B y,v
• 8 R B y
• 6 1 R A y,z,x,w
• gt 1 R A v,y

v
w
x
y
z
BI
72
Inference Tasks

• Knowledge is correct (captures intuitions)
• C subsumes D w.r.t. K iff for every model I of K,
  CI µ DI
• Knowledge is minimally redundant (no unintended
  synonyms)
• C is equivallent to D w.r.t. K iff for every
  model I of K, CI DI
• Knowledge is meaningful (classes can have
  instances)
• C is satisfiable w.r.t. K iff there exists some
  model I of K s.t. CI ?
• Querying knowledge
• x is an instance of C w.r.t. K iff for every
  model I of K, xI 2 CI
• hx,yi is an instance of R w.r.t. K iff for,
  every model I of K, (xI,yI) 2 RI
• Knowledge base consistency
• A KB K is consistent iff there exists some model
  I of K

73
OWL Reasoners

• DL Reasoner
• Using Tableaux algorithm
• FaCT, Racer (written in Common LISP)
• Decidability vs. Efficiency
• Rule-based Reasoner
• Using rule engine (Forward/Backward chaining)
• Describing OWL semantics as a rule base
• JESS (written in Java)
• Logic-based Reasoner
• Using theorem proving (Resolution), eg. Vampire
• Describing OWL semantics as a logic program
• JTP (written in Java)

74
Outline

• Introduction Motivation
• XML RDF
• RDFS
• DL
• OWL
• Future look and Resources

75
Future
And here, too
You will be here
76
Rule

• antecedent ? consequent
• If A fatherOf B, A brotherOf C then C uncleOf B
• father(?x,?y) ? brother(?y,?z) ? uncle(?x,?z)
• FOL, not DL, and is undecidable
• Very active research topic this year
• SWRL http//www.daml.org/2003/11/swrl/
• RuleML http//www.ruleml.org/
• Workshop_at_ ISWC2004 http//2004.ruleml.org/

77
Trust

• If one person says that x is blue, and another
  says that x is not blue, doesn't the whole
  Semantic Web fall apart?
• No!
• Applications on the Semantic Web will depend on
  context,
• Nonmonotonic reasoning can be applied.
• We will have proof checking mechanisms, and
  digital signatures.
• Proof Languages a language that let's us prove
  whether or not a statement is true
• Still missing at this moment

78
Resource Whos who
A very incomplete list, only some of whose work
is related to us
James A. Hendler
Ian Horrocks
Natasha Noy
Deborah McGuinness
Frank van Harmelen
Tim Berners-Lee
Jeff Heflin
Dieter A. Fensel
79
Resource Whos who
A very incomplete list, only some of whose work
is related to us
Heiner Stuckenschmidt's
Steffen Staab
Jérôme Euzenat
Ying Ding
Jeremy Carroll
Luciano Serafini
Paolo Bouquet
York Sure
80
Resources - Projects

• US
• DAML http//www.daml.org/
• Mindswap http//www.mindswap.org/
• Protege http//protege.stanford.edu/
• HayStack http//haystack.lcs.mit.edu/
• International
• RACER http//www.sts.tu-harburg.de/r.f.moeller/ra
  cer/
• Portal
• SemanticWeb http//www.semanticweb.org
• SemWebCentral http//projects.semwebcentral.org/
• SIGSEMIS http//www.sigsemis.org/

81
Resources - Projects

• EU
• On-To-Knowledge http//www.ontoknowledge.org/
  99-02
• OntoWeb http//www.ontoweb.org/ 01-04
• WonderWeb http//wonderweb.semanticweb.org 02-04
• Knowledge Web http//knowledgeweb.semanticweb.org/
  04-08
• SWAD-Europe http//www.w3.org/2001/sw/Europe/
• SEKT http//www.sekt-project.com/ 04-07
• Sesame http//www.openrdf.org/
• KAON http//kaon.semanticweb.org/
• FaCT http//www.cs.man.ac.uk/horrocks/FaCT/
• SWAP http//swap.semanticweb.org/
• SWWS http//swws.semanticweb.org/

82
Resources Standards and de facto standards

• XML http//www.w3.org/XML/
• RDF http//www.w3.org/RDF/
• OWL http//www.w3.org/2001/sw/WebOnt/
• DAMLOILhttp//www.daml.org/2001/03/damloil-inde
  x.html
• RDQLhttp//www.w3.org/Submission/RDQL/
• SWRL http//www.daml.org/2003/11/swrl/
• Jena http//jena.sourceforge.net/

83
Resources - Conferences

• WWW World Wide Web
• ESWC European Semantic Web Conference
• DL Description Logics
• ISWC International Semantic Web Conference
• SWDB Semantic Web and Databases
• KR Knowledge Representation and Reasoning
• SWEB Semantic Web Technologies in Electronic
  Business
• Protege Protege conference
• DC Dublin Core
• WI IEEE/WIC/ACM Web Intelligence
• Semantic Technology Conference

http//www.w3.org/Search/Mail/Public/search?type-i
ndexwww-rdf-interestindex-typetkeywordsCFP ht
tp//groups.yahoo.com/group/semanticweb/messagesea
rch?querycfp
84
Questions
85
backup
86
What information can we see

• WWW2002
• The eleventh international world wide web
  conference
• Sheraton waikiki hotel
• Honolulu, hawaii, USA
• 7-11 may 2002
• 1 location 5 days learn interact
• Registered participants coming from
• australia, canada, chile denmark, france,
  germany, ghana, hong kong, india, ireland, italy,
  japan, malta, new zealand, the netherlands,
  norway, singapore, switzerland, the united
  kingdom, the united states, vietnam, zaire
• Register now
• On the 7th May Honolulu will provide the backdrop
  of the eleventh international world wide web
  conference. This prestigious event
• Speakers confirmed
• Tim berners-lee
• Tim is the well known inventor of the Web,
• Ian Foster
• Ian is the pioneer of the Grid, the next
  generation internet

87
What information can we see
88
What information can a machine see

• WWW2002
• The eleventh international world wide web
  conference
• Sheraton waikiki hotel
• Honolulu, hawaii, USA
• 7-11 may 2002
• 1 location 5 days learn interact
• Registered participants coming from
• australia, canada, chile denmark, france,
  germany, ghana, hong kong, india, ireland, italy,
  japan, malta, new zealand, the netherlands,
  norway, singapore, switzerland, the united
  kingdom, the united states, vietnam, zaire
• Register now
• On the 7th May Honolulu will provide the backdrop
  of the eleventh international world wide web
  conference. This prestigious event
• Speakers confirmed
• Tim berners-lee
• Tim is the well known inventor of the Web,
• Ian Foster
• Ian is the pioneer of the Grid, the next
  generation internet

89
Solution XML markup with meaningful tags?

• ltnamegtWWW2002
• The eleventh international world wide
  webconlt/namegt
• ltlocationgtSheraton waikiki hotel
• Honolulu, hawaii, USAlt/locationgt
• ltdategt7-11 may 2002lt/dategt
• ltslogangt1 location 5 days learn interactlt/slogangt
• ltparticipantsgtRegistered participants coming from
• australia, canada, chile denmark, france,
  germany, ghana, hong kong, india, ireland, italy,
  japan, malta, new zealand, the netherlands,
  norway, singapore, switzerland, the united
  kingdom, the united states, vietnam,
  zairelt/participantsgt
• ltintroductiongtRegister now
• On the 7th May Honolulu will provide the backdrop
  of the eleventh international world wide web
  conference. This prestigious event
• Speakers confirmedlt/introductiongt
• ltspeakergtTim berners-leelt/speakergt
• ltbiogtTim is the well known inventor of the
  Web,lt/biogt

90
But What About

• ltconfgtWWW2002
• The eleventh international world wide
  webconlt/confgt
• ltplacegtSheraton waikiki hotel
• Honolulu, hawaii, USAlt/placegt
• ltdategt7-11 may 2002lt/dategt
• ltslogangt1 location 5 days learn interactlt/slogangt
• ltparticipantsgtRegistered participants coming from
• australia, canada, chile denmark, france,
  germany, ghana, hong kong, india, ireland, italy,
  japan, malta, new zealand, the netherlands,
  norway, singapore, switzerland, the united
  kingdom, the united states, vietnam,
  zairelt/participantsgt
• ltintroductiongtRegister now
• On the 7th May Honolulu will provide the backdrop
  of the eleventh international world wide web
  conference. This prestigious event
• Speakers confirmedlt/introductiongt
• ltspeakergtTim berners-leelt/speakergt
• ltbiogtTim is the well known inventor of the Web,

91
Machine sees

• ltnamegtWWW2002
• The eleventh international world wide webclt/namegt
• ltlocationgtSheraton waikiki hotel
• Honolulu, hawaii, USAlt/locationgt
• ltdategt7-11 may 2002lt/dategt
• ltslogangt1 location 5 days learn interactlt/slogangt
• ltparticipantsgtRegistered participants coming from
• australia, canada, chile denmark, france,
  germany, ghana, hong kong, india, ireland, italy,
  japan, malta, new zealand, the netherlands,
  norway, singapore, switzerland, the united
  kingdom, the united states, vietnam,
  zairelt/participantsgt
• ltintroductiongtRegister now
• On the 7th May Honolulu will provide the backdrop
  of the eleventh international world wide web
  conference. This prestigious event
• Speakers confirmedlt/introductiongt
• ltspeakergtTim berners-leelt/speakergt
• ltbiogtTim is the well known inventor of the
  Wlt/biogt
• ltspeakergtIan Fosterlt/speakergt
• ltbiogtIan is the pioneer of the Grid, the nelt/biogt