An introduction to the OWL ontology language and ontology editing with Protégé. Slides for the PhD Course on Semantic Web (http://elite.polito.it/).

1. Ontology languages

2. RDF / RDF Schema
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3. RDF Schema example
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4. RDFS problems
bl
RDFS is too “weak” to describe resources
with a suitable level of details
range and domain cannot be localized (e.g.
the range of hasChild is a person when
applied to a person, elephant when applied to
an elephant)
no constraints on existence or cardinality (e.g.
all instances of persons have one and only
one mother which is a person, and have
exactly two parents)
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5. RDFS problems
it is not possible to define transitive, inverse
or symmetrical statements (e.g. p of is a
y ( g part
transitive property, hasPart is the inverse of
isPartOf, touches is symmetrical)
, y )
Reasoning is not well supported
Non t d d
N standard semantics, no native reasoner
ti ti
exists
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6. Requirements for an ontology
language
g g
Extend existing Web standards
XML, RDF, RDFS, ...
Easy t understand and t use
E to d t d d to
based on well known KR languages
Formally specified
Adequate expressive power
Adeq ate e pressi e po er
Automatic support for reasoning
pp g
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7. Stack of Web languages
W3C
IST EU project
OntoKnowledgeg OWL
bioinformatics DARPA
University of OIL DAML+OIL
community
Washington
XOL SHOE OML RDF(S)
University of
y
Maryland XML
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8. Ontology Web Language (OWL)
O t l W bL
4th level on the semantic web cake
le el eb
Built on top of
p
XML
RDF/S
Three versions
Lite
DL (maps to Description Logic)
Full (not fully tractable)
Serializable
S i li bl as XML
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9. Ontology Web Language (OWL)
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10. OWL-DL
OWL DL
Based on Description Logic
Well defined formal semantics
well defined rules to treat sentence meaning
well defined assumptions on the world being
p g
modeled
Well known reasoning/inferencing
g g
algorithms
tractable,
tractable conclusions can be derived in finite
time
Widely available reasoning systems
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11. Building blocks in OWL
Ontology declaration (XML syntax)
<rdf:RDF xmlns:owl =http://www.w3.org/2002/07/owl#"
xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
l df "h // 3 /1999/02/22 df #"
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
xmlns:xsd ="http://www.w3.org/2001/XMLSchema#">
Ontology metadata (information about the
ontology)
<owl:Ontology rdf:about="">
<rdfs:comment>An example OWL ontology</rdfs:comment>
<owl:priorVersion
< l i V i
rdf:resource="http://www.mydomain.org/uni-ns-old"/>
<owl:imports
rdf:resource="http://www.mydomain.org/persons"/>
p y g p
<rdfs:label>University Ontology</rdfs:label>
</owl:Ontology>
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12. Classes
Cl
Every class i a d
E l is descendant of
d t f
owl:Thing
g
Classes are defined using
owl:Class
<owl:Class rdf:ID="Vehicle"/>
Equivalence
owl:equivalentClass
<owl:Class rdf:ID="Car">
<owl:equivalentClass rdf:resource="#Automobile"/>
q
</owl:Class>
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13. Subsumption
Provided by
owl:subClassOf
<owl:Class rdf:ID="2-Wheel-Drive">
< l Cl df ID "2 Wh l D i ">
<rdfs:subClassOf rdf:resource="#Car"/>
</owl:Class>
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14. Partitions
Disjoint partition
owl:disjointWith
<owl:Class rdf:about="#2-Wheel-Drive">
<owl:disjointWith
rdf:resource="#4-Wheel-Drive"/>
</owl:Class>
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15. Partitions
Exhaustive partition
owl:oneOf
<owl:Class rdf:ID="Car">
<owl:oneOf rdf:parseType="Collection">
<owl:Thing rdf:about="#2-Wheel-Drive"/>
g # /
<owl:Thing rdf:about="#4-Wheel-Drive"/>
</owl:oneOf>
</owl:Class>
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16. Attributes
A ib
Known also as “properties”
Datatype properties
Attributes that specify a class features by
means of data (XSD datatype)
Phone, title, age
Object properties
Attributes that define relationships between
classes (Relations)
isTaughtBy(Class(course), Class(professor))
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17. Datatype properties
Allow to describe a specific aspect of a
concept
Based on XSD data types
The range specifies the data type
The domain specifies the class to which the
property is referred
<owl:DatatypeProperty rdf:ID="age">
<rdfs:domain rdf:resource="#Person"/>
< df d i df "#P "/>
<rdfs:range rdf:resource="http://www.w3.org/2001/
XMLSchema#nonNegativeInteger"/>
</owl:DatatypeProperty>
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18. Relationships
Directed
From one concept to another, no viceversa
Defined through object properties
Domain: the class(es) from which the relation
departs
Range: the relation destination(s)
Subsumption between relationships is
possible
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19. Relationships
Example
<owl:ObjectProperty rdf:ID="isTaughtBy">
<rdfs:domain rdf:resource="#course"/>
<rdfs:range rdf:resource="#academicStaffMember"/>
<rdfs:subPropertyOf rdf:resource="#involves"/>
</owl:ObjectProperty>
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20. Instances (individuals)
I t (i di id l )
No i
N unique name assumption i OWL
ti in
If two instances have a different name or ID
this does not imply that they are different
individuals
E.g.: “Queen Elizabeth”, “The Queen” and
“Elizabeth Windsor” might all refer to the
g
same individual
It must be explicitly stated that individuals are
the same as each other, or different to each
other
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21. Instances (individuals)
I t (i di id l )
Defined by
D fi d b means of
f
rdf:Description + rdf:Type
p yp
<academicStaffMember rdf:ID="949352">
rdf:ID= 949352 >
<uni:age rdf:datatype="&xsd;integer">
39
</uni:age>
</academicStaffMember>
<rdf:Description rdf:ID="949353">
<rdf:type rdf:resource="#academicStaffMember"/>
</rdf:Description>
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22. Advanced constructs
Ad d t t
OWL supports several advanced constructs to
define classes and relationships
Intensional definition of classes
By defining constraints on attribute values (
y g (either
object or datatype properties)
<owl:Class rdf:about="#academicStaffMember">
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#teaches"/>
<owl:someValuesFrom
< l V l F
rdf:resource="#undergraduateCourse"/>
</owl:Restriction>
</rdfs:subClassOf>
</owl:Class>
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23. Advanced constructs
Ad d t t
Cardinality
Used to fix the number of instances that can be
related
E.g.: a department should have at least 10 members
<owl:Class rdf:about="#department">
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasMember"/>
<owl:minCardinality
rdf:datatype="&xsd;nonNegativeInteger"> 10
</owl:minCardinality>
</owl:Restriction>
</rdfs:subClassOf>
</owl:Class>
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24. Special properties
S i l ti
owl:TransitiveProperty
defines a transitive property, such as “has better
grade than”, “is taller than”, or “is ancestor of”
owl:SymmetricProperty
defines a symmetric property, such as “has same
grade as” or “is sibling of”
owl:FunctionalProperty
defines a property that has at most one value for
each object, such as “age”, “height”, or
“directSupervisor”
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25. Special properties
owl:InverseFunctionalProperty
defines a property for which two different
objects cannot have the same value
j
E.g.: the property
“isTheSocialSecurityNumberFor”: a social
isTheSocialSecurityNumberFor :
security number is assigned to one person
only
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26. OWL class constructors
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27. OWL axioms
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28. OWL: h t f ?
OWL what for?
To build an ontology
define classes and provide information on them
p
define properties and provide information on
them
To express facts about a domain
provide information on instances (individuals)
To reason about ontologies and facts
discover consequences of what is expressly
stated
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29. Example of ontology
p gy
building in OWL
with P té é
ith Protégé

30. Protégé
Open source ontology editor
Developed by Stanford Center for
Biomedical Informatics Research at the
Stanford University School of Medicine
http://protege.stanford.edu/
htt // t t f d d /
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31. F. Corno, L. Farinetti - Politecnico di Torino 31

32. Project steps
0. Conceptual design of the ontology
1. Classes definition
2.
2 Properties definition
3. Individuals definition
4. Restrictions definition
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33. Step 0
Conceptual design of the ontology
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34. Bed&Breakfast OneStarRating
hasRating Accommodation
Rating
Accommodation TwoStarRating
Camping
Budget ThreeStarRating
Accommodation
Hotel
int
hasZipCode
hasAccommodation
Luxury Hotel string
Backpacker Contact
Hiking Destination hasStreet
Surfing hasEMail
Sheraton hasContact
C string
Sports isOffered
Destination
Yoga Beach
Activity Caprera
hasCity
Relaxation
hasActivity
Quiet string
Destination Family
Destination Gallipoli
Sunbathing
Adventure Sightseeing
Bardonecchia
Rimini
Safari
BunjeeJumping
Museums
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35. Step 1a
Define classes and subclasses
Is-a relationship, or subsumption
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36. Bed&Breakfast
Accommodation
Rating
Accommodation
Camping
Budget
Accommodation
Hotel
Luxury Hotel
Backpacker Contact
Hiking Destination
Surfing
Sports
Destination
Yoga Beach
Activity
Relaxation
Quiet
Destination Family
Destination
Sunbathing
Adventure Sightseeing
Safari
BunjeeJumping
Museums
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37. OWL code
<owl:Class rdf:ID="Camping">
<rdfs:subClassOf>
<owl:Class rdf:ID="Accommodation"/>
rdf:ID Accommodation />
</rdfs:subClassOf>
</owl:Class>
<owl:Class rdf:ID="BudgetAccommodation">
<rdfs:subClassOf rdf:resource #Accommodation />
rdf:resource="#Accommodation"/>
</owl:Class>
<owl:Class rdf:ID="BedAndBreakfast">
<rdfs:subClassOf rdf:resource="#Accommodation"/>
</owl:Class>
<owl:Class rdf:ID="LuxuryHotel">
<rdfs:subClassOf>
<owl:Class rdf:ID="Hotel"/>
</rdfs:subClassOf>
</owl:Class>
<owl:Class rdf:about="#Hotel">
<rdfs:subClassOf rdf:resource="#Accommodation"/>
</owl:Class>
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38. Step 1b
Disjoint
Define disjoint Bed&Breakfast
classes Accommodation
Camping
Budget
Accommodation
Hotel
<owl:Class rdf:about="#Hotel">
<owl:disjointWith rdf:resource="#Camping"/>
<owl:disjointWith>
<owl:Class rdf:about="#BedAndBreakfast"/>
</owl:disjointWith>
<rdfs:subClassOf rdf:resource="#Accommodation"/>
</owl:Class>
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39. Step 1c Activity
Adventure Sightseeing
Define multiple
Safari
inheritance BunjeeJumping
Museums
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40. Step 2a Accommodation
Range
Define object properties hasAccommodation
relationships Domain
Destination
<owl:ObjectProperty rdf:ID="hasAccommodation">
<rdfs:domain rdf:resource="#Destination"/>
<rdfs:range rdf:resource="#Accommodation"/>
</owl:ObjectProperty>
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41. Step 2b
Define object properties characteristics
E.g:
E g: define an inverse object property
isOffered
Destination
Activity
hasActivity
<owl:ObjectProperty rdf:about #isOffered >
rdf:about="#isOffered">
<rdfs:range rdf:resource="#Destination"/>
<owl:inverseOf rdf:resource="#hasActivity"/>
<rdfs:domain rdf:resource="#Activity"/>
</owl:ObjectProperty>
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42. int
Step 2c
hasZipCode
string
Contact
hasStreet
hasEMail string
Define datatype properties
The range specifies the
data type
yp
<owl:DatatypeProperty rdf:ID="hasEMail">
<rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#string"/>
<rdfs:domain rdf:resource="#Contact"/>
/owl:DatatypeProperty
</owl:DatatypeProperty>
<owl:DatatypeProperty rdf:ID="hasZipCode">
<rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#int"/>
<rdfs:domain rdf:resource="#Contact"/>
</owl:DatatypeProperty>
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43. Step 3 Accommodation
OneStarRating
Rating
g
TwoStarRating
Define individuals ThreeStarRating
instances Family
Destination
Bardonecchia
Rimini
<AccommodationRating rdf:ID="OneStarRating"/>
<AccommodationRating rdf:ID="ThreeStarRating"/>
<AccommodationRating rdf:ID="TwoStarRating"/>
<FamilyDestination rdf:ID="Bardonecchia"/>
<F il D ti ti df ID "B d hi "/>
<FamilyDestination rdf:ID="Rimini"/>
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44. Step 4
Define restrictions
To restrict the individuals that belong to a
class
Quantifier restrictions (existential, universal
quantifiers)
Cardinality restrictions
hasValue
h V l restrictions
t i ti
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45. Step 4 – example 1 Accommodation
hasAccommodation >= 1
Activity
FamilyDestination is a Destination
Destination ith t least one
D ti ti with at l t hasActivity >= 2
accommodation and at least
Family
2 activities Destination
Necessary and
sufficient condition
Cardinality restriction
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46. FamilyDestination is a
Step
St 4 – example 1
l Destination with at least
one accommodation and
<owl:Class rdf:ID= FamilyDestination >
rdf:ID="FamilyDestination"> at least 2 activities
<owl:equivalentClass>
<owl:Class>
<owl:intersectionOf rdf:parseType="Collection">
<owl:Restriction>
<owl:onProperty>
<owl:ObjectProperty rdf:ID="hasAccommodation"/>
</owl:onProperty>
<owl:minCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#int"
>1</owl:minCardinality>
/ i i i
</owl:Restriction>
<owl:Restriction>
<owl:minCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#int"
>2</owl:minCardinality>
<owl:onProperty>
<owl:ObjectProperty rdf:ID="hasActivity"/>
</owl:onProperty>
</owl:Restriction>
<owl:Class rdf:about="#Destination"/>
</owl:intersectionOf>
</owl:Class>
</owl:equivalentClass>
</owl:Class>
/
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47. Step 4 – example 2
QuietDestination is a Destination Destination
that is t h
th t i not chosen b noisy
by i
families Quiet
Destination Family
Destination
Complement restriction
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48. Step
St 4 – example 2
l QuietDestination is a
Destination that is not
chosen by noisy families
<owl:Class rdf:ID="QuietDestination">
<owl:equivalentClass>
<owl:Class>
<owl:intersectionOf rdf:parseType="Collection">
<owl:Class>
<owl:complementOf rdf:resource="#FamilyDestination"/>
</owl:Class>
<owl:Class rdf:about="#Destination"/>
</owl:intersectionOf>
</owl:Class>
</owl:equivalentClass>
</owl:Class>
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49. OneStarRating
Step
St 4 – example 3
l Accommodation
Rating
TwoStarRating
Bed&Breakfast
ThreeStarRating
Budget
hasRating
Accommodation Camping
Accommodation
BudgetAccommodation is
Luxury Hotel
an Accommodation that has Hotel
either one or two star rating
g Sheraton
Existential restriction
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50. Step
St 4 – example 3
l BudgetAccommodation
is an Accommodation
that has either one or
<owl:Class rdf:ID "BudgetAccommodation">
rdf:ID="BudgetAccommodation"> two star rating
t t ti
<owl:equivalentClass>
<owl:Class>
<owl:intersectionOf rdf:parseType="Collection">
<owl:Restriction>
<owl:onProperty>
<owl:ObjectProperty rdf:ID="hasRating"/>
</owl:onProperty>
<owl:someValuesFrom>
<owl:Class>
<owl:oneOf rdf:parseType="Collection">
<AccommodationRating rdf:ID="OneStarRating"/>
<AccommodationRating rdf:ID= TwoStarRating />
rdf:ID="TwoStarRating"/>
</owl:oneOf>
</owl:Class>
</owl:someValuesFrom>
</owl:Restriction>
<owl:Class rdf:about="#Accommodation"/>
</owl:intersectionOf>
</owl:Class>
</owl:equivalentClass>
</owl:Class>
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51. Bed&Breakfast
B d&B kf t
Hotel
Step 4 – example 4 Camping
Accommodation
Budget
BackpackerDestination Accommodation
hasAccommodation
is a Destination that Backpacker
Sports Destination
hasActivity
provides budget
accommodation and Relaxation Activity Destination
offers sport or
ff t
Adventure
adventure activities Sightseeing
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52. BackpackerDestination is
p
Step 4 – example 4 a Destination that provides
budget accommodation
<owl:Class rdf:ID="BackpackerDestination"> and offers sport or
<owl:equivalentClass> adventure activities
<owl:Class>
<owl:intersectionOf rdf:parseType="Collection">
<owl:Restriction>
<owl:onProperty>
<owl:ObjectProperty rdf:ID="hasAccommodation"/>
</owl:onProperty>
<owl:someValuesFrom rdf:resource="#BudgetAccommodation"/>
</owl:Restriction>
<owl:Class rdf:about="#Destination"/>
< l Cl df b t "#D ti ti "/>
<owl:Restriction>
<owl:onProperty>
<owl:ObjectProperty rdf:ID="hasActivity"/>
</owl:onProperty>
<owl:someValuesFrom>
<owl:Class>
<owl:unionOf rdf:parseType="Collection">
<owl:Class rdf:about="#Sports"/>
<owl:Class rdf:about #Adventure />
rdf:about="#Adventure"/>
</owl:unionOf>
</owl:Class>
</owl:someValuesFrom>
</owl:Restriction>
</owl:intersectionOf>
</owl:Class>
</owl:equivalentClass>
F. Corno, L. Farinetti - Politecnico di Torino
</owl:Class> 52

53. License
This work is licensed under the Creative
Commons Attribution-Noncommercial-
Share Alike 3.0 Unported License.
To view a copy of this license visit
license,
http://creativecommons.org/licenses/by-
nc-sa/3.0/ or send a letter to C
/3 0/ Creative
Commons, 171 Second Street, Suite 300,
San Francisco, California, 94105, USA.
F. Corno, L. Farinetti - Politecnico di Torino 53