OWL
Dr. Alexandra I. Cristea
http://www.dcs.warwick.ac.uk/~acristea/
Once upon a time…
“Wholly new forms of encyclopedias will
appear, ready-made with a mesh of
associative trails running through them,
ready to be dropped into the memex and
there amplified.”
Vannevar Bush - As we may Think, July
1945
2
Semantic Web
I have a dream for the Web [in which
computers] become capable of analyzing all
the data on the Web – the content, links, and
transactions between people and computers.
“a web
of data
can
be this
A "Semantic
Web",
which that
should
make
possible, has
yet to emerge,
but and
when it
processed
directly
does, the day-to-day mechanisms of trade,
indirectly
machines”
bureaucracy
and our by
daily
lives will be
handled by machines talking to machines.
The "intelligent agents" people have touted
for ages will finally materialize.
3
The SW stack (1.0, by TBL, 2000)
4
The SW stack (by Steve Bratt, 2007)
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[W3.org] (reminder)
• Extensible Markup Language (XML) is a
simple, very flexible text format
• Uniform Resource Identifiers (URIs, aka
URLs) are short strings that identify
resources in the web
• The Resource Description Framework
(RDF) is a general-purpose language
for representing information in the Web.
6
[W3.org]
• RDF Schema, is a semantic extension
of RDF.
• OWL facilitates:
– greater machine interpretability of Web
content than that supported by XML, RDF,
and RDF Schema (RDF-S)
– by providing additional vocabulary
– along with a formal semantics.
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What is OWL?
•
W3C Recommendation, February 2004.
–
–
–
•
•
•
•
•
web standard
Newest OWL 2 (W3C Recommendation 11 December
2012)
http://www.w3.org/TR/owl2-overview/
Web Ontology Language
originally built on top of RDF
for processing information on the web
designed to be interpreted by computers, not for
being read by people
OWL and a version of OWL2 are written in XML
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Why OWL?
• OWL is a part of the "Semantic Web Vision" - a
future where:
– Web information has exact meaning
– Web information can be processed by computers
– Computers can integrate information from the web
• OWL was designed to
– provide a common way to process the content of web
information (instead of displaying it).
– be read by computer applications (instead of humans).
10
What is an Ontology? (reminder)
• formal specification of a certain domain
• machine manipulable model
• Ontology is about the exact description of things and
their relationships and an inference mechanism for it.
• For the web, ontology is about
– the exact description of web information and
– relationships between web information and
– reasoning with it.
• dictionary  taxonomy  ontology
11
History of OWL
• Based on predecessors
– (OWL DL = ¼ DAML+OIL)
• A Web Language: Based on RDF(S)
• An Ontology Language: Based on logic
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OWL is Different from RDF
• OWL , RDF similar
• but OWL
– stronger language
– greater machine interpretability
– larger vocabulary
– stronger syntax.
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OWL Sublanguages
• OWL has three sublanguages:
– OWL Lite
• hierarchy + simple constraints + cardinality {0,1}
– OWL DL (includes OWL Lite)
• complete, decidable (part of FOL; extends ALC)
• Type separations (class <> property <> individual)
• OWL DL is the subset of OWL (Full) that is optimized for reasoning
and knowledge modeling
– OWL Full (includes OWL DL)
• aug. meaning RDF.
• Classes - individuals
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OWL2 Profiles
• OWL 2 EL
– Polynomial time algorithms (standard reasoning)
– For very large ontologies
– Performance important; expressivity less
• OWL 2 QL
– Relat. Db. Queries in LogSpace (SQL)
– Lightweight ontologies, many individuals
• OWL 2 RL
– Polynomial time algorithms (rule-extended db. technol.)
– Lightweight ontologies; many individuals
– Operating directly on RDF
• All more restrictive than OWL DL
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OWL can be written in XML
• By using XML, OWL information can easily be
exchanged between different types of
computers using different types of operating
system and application languages.
• Oh yes, there is a namespace:
xmlns:owl ="http://www.w3.org/2002/07/owl#"
Note: OWL2 also written in the Manchester notation
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OWL Use Cases
• At least two different user groups
– OWL used as data exchange language
(define interfaces of services and agents)
– OWL used for terminologies or knowledge models
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OWL Example (Airport)
• Example: http://www.cs.man.ac.uk/~rector/Modules/CS6462004/Labs/Thursday/Simple_University-01.owl
• OWL Syntax converter:
http://mowl-power.cs.man.ac.uk:8080/converter/ (offline
currently)
• Validators:
RDF: http://www.w3.org/RDF/Validator/ (try it out)
OWL: http://mowl-power.cs.man.ac.uk:8080/validator/ (offline
currently)
Protégé: http://protege.stanford.edu/products.php#desktop-protege
• Semantic web search engine (for more OWL examples):
http://swoogle.umbc.edu/
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Relationship OWL 2, OWL 1
• OWL 2 has a very similar overall structure to OWL 1.
• backwards compatibility with OWL 1 is complete.
• New features with new expressivity:
– keys; property chains; richer datatypes, data ranges;
qualified cardinality restrictions;
– asymmetric, reflexive, and disjoint properties; and
– enhanced annotation capabilities
– Based on real applications, use cases and user experience
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Modelling Knowledge: basics
• OWL2: knowledge representation language
• Axioms: statements expressed in OWL ontology
• Entities: refer to real-world objects
• Expressions: combinations/ descriptions of entities
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OWL Ontologies
• What’s inside an OWL ontology (entities)
– Individuals
– Properties (Slots) / values
• Restrictions on properties (type, cardinality)
• Characteristics of properties (transitive, …)
– Classes + class-hierarchy
• Relations between classes (inheritance, disjoints, equivalents)
– Annotations
• Reasoning tasks: classification, consistency checking
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Last time:
• We revisited:
– the SW goals and
– the SW stack and its components
• discussed ontology languages in this context
– Reminded ourselves about the ontology definition
• Started OWL:
–
–
–
–
–
–
–
–
why, history,
OWL 1.1 vs. OWL2,
OWL1.1 sub-languages,
OWL2 Profiles,
Use Cases,
An Example,
how OWL 2 models knowledge,
OWL elements
26
Now:
• OWL/XML
– Starting with
• header
• elements
(parts of the universe)
• See also:
http://www.w3.org/TR/2012/REC-owl2rdf-based-semantics-20121211/
27
The OWL language
• There are different syntactic forms of OWL:
• – RDF/XML syntax see http://www.w3.org/TR/owl2-mapping-to-rdf/
(used for interchange: can be written and read by all conformant OWL 2 software)
• – OWL/XML syntax that does not follow the RDF conventions
(first of the languages) see http://www.w3.org/TR/owl2-xml-serialization/
• – functional syntax (used in the language specification document)
(much more compact and readable) see http://www.w3.org/TR/owl2-syntax/
• – graphic syntax based on the conventions of UML
(Unified Modelling Language)
(an easy way for people to become familiar with OWL)
• – Manchester syntax
(used in the Protégé editor) see http://www.w3.org/TR/owl2-manchester-syntax/
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Parts of the Universe (OWL2)
individuals
data values
ontologies
classes
datatypes
properties
rdfs:Resource
rdfs:Literal
owl:Ontology
rdfs:Class
rdfs:Datatype
rdf:Property
data properties
owl:DatatypeProperty
ontology properties
owl:OntologyProperty
annotation properties
owl:AnnotationProperty
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Structure of entities and literals in OWL2
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OWL
• Individuals (e.g., “FourSeasons”)
• Properties
– ObjectProperties (references)
– DatatypeProperties (simple values)
• Classes (e.g., “Hotel”)
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Individuals
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Individuals (Instances)
• Represent objects in the domain
• Specific things
• Two names could represent the same
“real-world” individual
Sydney
SydneysOlympicBeach
BondiBeach
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Example of Individuals
<Region rdf:ID="CentralCoastRegion" />
equivalent to:
<owl:Thing rdf:ID="CentralCoastRegion" />
<owl:Thing rdf:about="#CentralCoastRegion">
<rdf:type rdf:resource="#Region"/>
</owl:Thing>
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Homework task
• Identify individuals in an ontology of
your choice (either directly in
OWL/RDF, or in Protégé)
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Properties
• Object Properties
• Datatype Properties
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ObjectProperties
• Link two individuals together
• Relationships (0..n, n..m)
BondiBeach
Sydney
FourSeasons
41
Example Property
<owl:ObjectProperty rdf:ID=“hasPart">
<rdfs:domain rdf:resource="#Destination" />
<rdfs:range rdf:resource="#Beaches" />
</owl:ObjectProperty>
42
Property Domain & Range
• If a relation is:
subject_individual  hasProperty  object_individual
• The domain is the class of the subject individual
• The range is the class of the object individual (or a
datatype if hasProperty is a Datatype Property)
DomainClass
RangeClass
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Properties, Range and Domain
• Property characteristics
– Domain: “left side of relation” (Destination)
– Range: “right side” (Accomodation)
Accomodation
Destination
BestWestern
Sydney
FourSeasons
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Domains
• Individuals can only take values of
properties that have matching domain
– “Only Destinations can have Accommodations”
• Domain can contain multiple classes
• Domain can be undefined:
Property can be used everywhere
45
Property Restriction: Example Cardinality
<owl:Class rdf:ID="Wine">
<rdfs:subClassOf rdf:resource="&food;PotableLiquid"/>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource="#madeFromGrape"/>
<owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:minCardinality>
</owl:Restriction>
</rdfs:subClassOf> ...
</owl:Class>
<owl:Restriction>
<owl:onProperty rdf:resource="#madeFromGrape"/>
<owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:minCardinality
</owl:Restriction>
46
OWL Extends Other Ontologies
• extend existing ontology by saying things about terms in it:
<owl:Class rdf:about="#Animal">
<rdfs:comment>
Animals have exactly two parents, ie: If x is an animal, it has exactly 2
parents (but NOT anything that has 2 parents is an animal).
</rdfs:comment>
<rdfs:subClassOf>
<owl:Restriction owl:cardinality="2">
<owl:onProperty rdf:resource="#hasParent"/>
</owl:Restriction>
</rdfs:subClassOf>
</owl:Class>
• If ontology is already published, you use the full URL.
<owl:Class rdf:about="http://www.sample.com/ontologies/zoo#Animal">
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Restrictions (Overview)
• Define a condition for property values
–
–
–
–
–
–
allValuesFrom
someValuesFrom
hasValue
minCardinality
maxCardinality
cardinality
• An anonymous class consisting of all
individuals that fulfill the condition
57
Inverse Properties
• Represent bidirectional relationships
• Adding a value to one property also
adds a value to the inverse property (!)
BondiBeach
Sydney
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Inverse Property Example
<owl:ObjectProperty rdf:ID="hasPart">
<rdf:type rdf:resource="&owl;FunctionalProperty" />
</owl:ObjectProperty>
<owl:ObjectProperty rdf:ID=“isPartOf">
<owl:inverseOf rdf:resource="#hasPart" />
</owl:ObjectProperty>
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Transitive Properties
• If A is related to B and B is related to C
then A is also related to C
• Often used for part-of relationships
NewSouthWales
Sydney
BondiBeach
hasPart (derived)
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Transitive Property Example
<owl:ObjectProperty rdf:ID="locatedIn">
<rdf:type rdf:resource="&owl;TransitiveProperty" />
<rdfs:domain rdf:resource="&owl;Thing" /> < Is this necessary?
<rdfs:range rdf:resource="#Region" />
</owl:ObjectProperty>
<Region rdf:ID="SantaCruzMountainsRegion">
<locatedIn rdf:resource="#CaliforniaRegion" />
</Region>
What can be deduced?
<Region rdf:ID="CaliforniaRegion">
<locatedIn rdf:resource="#USRegion" />
</Region>
62
• Previously:
– Header of OWL
– Individuals in OWL
– Properties in OWL:
• Domain, range, restrictions, inverse, transitive
• Next:
– More on Properties (sub-properties,
datatype properties)
– Classes
63
Sub-properties Example
<owl:ObjectProperty rdf:ID="hasWineDescriptor">
<rdfs:domain rdf:resource="#Wine" />
<rdfs:range rdf:resource="#WineDescriptor" />
</owl:ObjectProperty>
<owl:ObjectProperty rdf:ID="hasColor">
<rdfs:subPropertyOf rdf:resource="#hasWineDescriptor"
/>
<rdfs:range rdf:resource="#WineColor" /> ...
</owl:ObjectProperty>
What can we say about some instance that has a hasColor property?
64
Homework task
• Identify different types of object
properties in an ontology of your choice
(either directly in OWL/XML, or in
Protégé). Find out their type.
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DatatypeProperties
• Link individuals to primitive values
(integers, floats, strings, Booleans etc)
• Often: AnnotationProperties without
formal “meaning” in OWL 1.1
Sydney
hasSize = 4,500,000
isCapital = true
rdfs:comment = “Don’t miss the opera house”
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XML Schema Datatypes in OWL
• OWL supports XML Schema primitive
datatypes
– E.g., integer, real, string, …
• Strict separation between “object” classes and
datatypes
– Disjoint interpretation domain for datatypes
– Disjoint “object” and datatype properties
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Why Separate Classes and
Datatypes?
• Philosophical reasons:
– Datatypes structured by built-in predicates
– Not appropriate to form new datatypes using ontology
language
• Practical reasons:
– Ontology language remains simple and compact
– Semantic integrity of ontology language not compromised
– Implementability not compromised — can use hybrid
reasoner
69
Homework task
• Identify datatype properties in an
ontology of your choice (either directly
in OWL/XML, or in Protégé)
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Classes
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Classes
• Sets of individuals with common
characteristics
• Individuals are instances of at least one
class
Beach
City
Sydney
Cairns
BondiBeach
CurrawongBeach
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• Classes are defined using the owl:class
element;
• owl:class is a subclass of rdfs:class
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Examples of Classes in OWL
<owl:Class rdf:ID="Winery"/>
<owl:Class rdf:ID="Region"/>
<owl:Class rdf:ID="ConsumableThing"/>
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Class membership
• Adam is a Person.
<Person rdf:ID="Adam">
<rdfs:label>Adam</rdfs:label>
<rdfs:comment>Adam is a person.
</rdfs:comment>
<age><xsd:integer rdf:value="13"/></age>
<shoesize><xsd:decimal
rdf:value="9.5"/></shoesize>
</Person>
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Superclass Relationships
• Classes can be organized in a hierarchy
• Direct instances of subclass are also
(indirect) instances of superclasses
Cairns
Sydney
Canberra
Coonabarabran
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Example Subclasses
<owl:Class rdf:ID="PotableLiquid">
<rdfs:subClassOf rdf:resource="#ConsumableThing" /> …
</owl:Class>
<owl:Class rdf:ID="Wine"> What can be said about wine here?
<rdfs:subClassOf rdf:resource="&food;PotableLiquid"/>
<rdfs:label xml:lang="en">wine</rdfs:label>
<rdfs:label xml:lang="fr">vin</rdfs:label> ...
</owl:Class>
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Class Relationships
• Classes can overlap arbitrarily
RetireeDestination
City
Cairns
BondiBeach
Sydney
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Class Disjointness
• All classes could potentially overlap
• In many cases we want to make sure
they don’t share instances
disjointWith
UrbanArea
Sydney
Sydney
City
RuralArea
Woomera
CapeYork
Destination
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Example disjoint
<owl:Class rdf:about="#Man">
<owl:disjointWith rdf:resource="#Woman"/>
</owl:Class>
not in OWL Lite!
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How do we say:
Lecturer is disjoint (different) from professor.
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How do we say:
Faculty is equivalent with academic staff.
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You could also use owl:disjointWith here.
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• Last time:
– Last of OWL properties (sub-properties,
datatype properties)
– OWL classes: disjoint, union, intersection,
equivalence, etc.
• Next:
– revisit reading OWL
– OWL2 properties
– Visualisation
– Final OWL considerations
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OWL Syntax
What does this mean?
<owl:Class>
<owl:intersectionOf rdf:parseType="collection">
<owl:Class rdf:about="#Person"/>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasChild"/>
<owl:allValuesFrom>
<owl:unionOf rdf:parseType="collection">
<owl:Class rdf:about="#Doctor"/>
<owl:Restriction>
<owl:onProperty rdf:resource="#hasChild"/>
<owl:hasClass rdf:resource="#Doctor"/>
</owl:Restriction>
</owl:unionOf>
</owl:allValuesFrom>
</owl:Restriction>
</owl:intersectionOf>
</owl:Class>
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Class Descriptions
• Define the “meaning” of classes
• Anonymous class expressions are used
– “All national parks have campgrounds.”
– “A backpackers destination is a destination
that has budget accommodation and offers
sports or adventure activities.”
• Expressions mostly restrict property
values (OWL Restrictions)
101
Restrictions (Reminder)
• Define a condition for property values
–
–
–
–
–
–
allValuesFrom
someValuesFrom
hasValue
minCardinality
maxCardinality
cardinality
• An anonymous class consisting of all
individuals that fulfill the condition
102
Homework task
• Identify different classes in an ontology
of your choice (either directly in
OWL/XML, or in Protégé);
• Identify relations between classes;
• Identify types of classes (including
anonymous classes).
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(reminder)
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and after
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Visualization of OWL
ontologies
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Protégé
• http://protege.cim3.net/file/pub/ontologie
s/travel/travel.owl
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Visualization with OWLViz
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Visualization in Ontograf
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Tourism Semantic Web (2)
OWL
Metadata
(Individuals)
Tourism Ontology
Destination
Activity Accommodation
Web Services
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OWL File & import
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
xmlns:owl="http://www.w3.org/2002/07/owl#"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:travel="http://protege.stanford.edu/plugins/
owl/owl-library/travel.owl#"
xml:base="http://protege.stanford.edu/plugins/owl/owllibrary/heli-bunjee.owl">
[. . .]
</rdf:RDF>
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OWL File: [. . .] OWL body in RDF wrap
<owl:Ontology rdf:about="">
<owl:imports rdf:resource="http://protege.stanford.edu/
plugins/owl/owl-library/travel.owl"/>
</owl:Ontology>
<owl:Class rdf:ID="HeliBunjeeJumping">
<rdfs:subClassOf rdf:resource="http://protege.stanford.
edu/plugins/owl/owl-library/travel.owl#BunjeeJumping"/>
</owl:Class>
<HeliBunjeeJumping rdf:ID="ManicSuperBunjee">
[***]
</HeliBunjeeJumping>
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OWL File [***] in HeliBunjeeJumping
<travel:isPossibleIn>
<rdf:Description rdf:about="http://protege.stanford.edu/plugins/owl/owllibrary/travel.owl#Sydney">
<travel:hasActivity rdf:resource="#ManicSuperBunjee"/>
</rdf:Description>
</travel:isPossibleIn>
<travel:hasContact>
[ +++ ]
</travel:hasContact>
<rdfs:comment rdf:datatype="http://www.w3.org/2001/XMLSchema#string">Manic
super bunjee now offers nerve wrecking jumps from 300 feet right out of a
helicopter. Satisfaction guaranteed.
</rdfs:comment>
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OWL File [+++] in travel:hasContact
<travel:Contact rdf:ID="MSBInc">
<travel:hasEmail rdf:datatype="http://www.w3.org/2001/XMLSchema#string">
msb@manicsuperbunjee.com
</travel:hasEmail>
<travel:hasCity rdf:datatype="http://www.w3.org/2001/XMLSchema#string">
Sydney
</travel:hasCity>
<travel:hasStreet rdf:datatype="http://www.w3.org/2001/XMLSchema#string">
Queen Victoria St
</travel:hasStreet>
<travel:hasZipCode rdf:datatype="http://www.w3.org/2001/XMLSchema#int">
1240
</travel:hasZipCode>
</travel:Contact>
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Problems with RDFS (reminder)
RDFS too weak to describe resources in sufficient detail
– No localised range and domain constraints
• Can’t say that the range of hasChild is person when applied to
persons and elephant when applied to elephants
– No existence/cardinality constraints
• Can’t say that all instances of person have a mother that is also a
person, or that persons have exactly 2 parents
– No transitive, inverse or symmetrical properties
• Can’t say that isPartOf is a transitive property, that hasPart is the
inverse of isPartOf or that touches is symmetrical
Difficult to provide reasoning support
– No “native” reasoners for non-standard semantics
– May be possible to reason via FO axiomatisation
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Homework
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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
128
From RDF to OWL (history)
• Two languages developed to satisfy above requirements
– OIL: developed by group of (largely) European researchers (several from
EU OntoKnowledge project)
– DAML-ONT: developed by group of (largely) US researchers (in DARPA
DAML programme)
• Efforts merged to produce DAML+OIL
– Development was carried out by “Joint EU/US Committee on Agent
Markup Languages”
– Extends (“DL subset” of) RDF
• DAML+OIL submitted to W3C as basis for standardisation
– Web-Ontology (WebOnt) Working Group formed
– WebOnt group developed OWL language based on DAML+OIL
– OWL language became thus a W3C Proposed Recommendation
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OWL Language
• Three species of OWL
– OWL full is union of OWL syntax and RDF
– OWL DL restricted to FOL fragment (¼ DAML+OIL)
– 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
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–
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Well defined semantics
Formal properties well understood (complexity, decidability)
Known reasoning algorithms
Implemented systems (highly optimised)
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• Thus, OWL DL was used as basis of the
OWL2 profiles:
– OWL EL ,
– OWL QL ,
– OWL RL
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OWL Lite Synopsis
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RDF Schema
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Features:
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Class (Thing, Nothing)
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rdfs:subClassOf
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rdf:Property
rdfs:subPropertyOf
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rdfs:domain
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rdfs:range
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Individual
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(In)Equality:
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equivalentClass
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equivalentProperty
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sameAs
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differentFrom
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AllDifferent
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distinctMembers
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Property Characteristics:
ObjectProperty
DatatypeProperty
inverseOf
TransitiveProperty
SymmetricProperty
FunctionalProperty
InverseFunctionalProperty
Property Restrictions:
Restriction
onProperty
allValuesFrom
someValuesFrom
Restricted Cardinality:
minCardinality (only 0 or 1)
maxCardinality (only 0 or 1)
cardinality (only 0 or 1)
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Header Information:
Ontology
imports
Class Intersection:
intersectionOf
Versioning:
versionInfo
priorVersion
backwardCompatibleW
ith
incompatibleWith
DeprecatedClass
DeprecatedProperty
Annotation
Properties:
rdfs:label
rdfs:comment
rdfs:seeAlso
rdfs:isDefinedBy
AnnotationProperty
OntologyProperty
Datatypes
xsd datatypes
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OWL DL + Full
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Class Axioms:
oneOf, dataRange
disjointWith
equivalentClass
(applied to class expressions)
rdfs:subClassOf
(applied to class expressions)
Boolean Combinations of Class Expressions:
unionOf
complementOf
intersectionOf
Arbitrary Cardinality:
minCardinality
maxCardinality
cardinality
Filler Information:
hasValue
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OWL built-in classes
• owl:FunctionalProperty,
owl:InverseFunctionalProperty,
owl:SymmetricProperty,
owl:TransitiveProperty,
owl:DeprecatedClass,
owl:DeprecatedProperty
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OWL built in properties
• owl:equivalentClass, owl:disjointWith,
owl:equivalentProperty, owl:inverseOf, owl:sameAs,
owl:differentFrom, owl:complementOf, owl:unionOf,
owl:intersectionOf, owl:oneOf, owl:allValuesFrom,
owl:onProperty, owl:someValuesFrom,
owl:hasValue, owl:minCardinality,
owl:maxCardinality, owl:cardinality,
owl:distinctMembers
• annotation properties: owl:versionInfo, rdfs:label,
rdfs:comment, rdfs:seeAlso, rdfs:isDefinedBy
• ontology properties: owl:imports, owl:priorVersion,
owl:backwardCompatibleWith, owl:incompatibleWith
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OWL query language: OWL-QL
• OWL Query Language (OWL-QL) is an
updated version of the DAML Query
Language (DQL).
• It is intended to be a candidate standard
language and protocol for queryanswering dialogues among Semantic
Web computational agents.
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OWL Class Constructors
• XMLS datatypes as well as classes in
• arbitrarily complex nesting of constructors
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OWL Axioms
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OWL Conclusion
• We have learned:
– OWL definition
– OWL comparison with RDF
– OWL classes and properties
– Usage scenarios
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