1 resource description framework: rdf rdf schema sparql based on slides by: grigoris antoniou frank...
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Resource Description Framework:
RDFRDF Schema
SPARQLBased on Slides By:Grigoris Antoniou
Frank van Harmelen
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Semantic Web Layers
XML layer Syntactic basis
RDF layer RDF basic data model for facts RDF Schema simple ontology language
Ontology layer More expressive languages than RDF
Schema Current Web standard: OWL
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Resources
We can think of a resource as an object, a “thing” we want to talk about E.g. authors, books, publishers, places,
people, hotels Every resource has a URI, a Universal
Resource Identifier A URI can be
a URL (Web address) or some other kind of unique identifier
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Properties
Properties are a special kind of resources
They describe relations between resources E.g. “written by”, “age”, “title”, etc.
Properties are also identified by URIs Advantages of using URIs:
Α global, worldwide, unique naming scheme
Reduces the homonym problem of distributed data representation
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Statements
Statements assert the properties of resources
A statement is an subject-predicate-object triple It consists of a resource, a property,
and a value Values can be resources or literals
Literals are atomic values (strings)
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Example RDF Structure
<rdf:Description rdf:ID="CIT1111"><rdf:type rdf:resource=
"http://www.mydomain.org/uni-ns#course"/>
<uni:courseName>Discrete Maths</uni:courseName>
<uni:isTaughtBy rdf:resource="#949318"/></rdf:Description>
<rdf:Description rdf:ID="949318"><rdf:type rdf:resource=
"http://www.mydomain.org/uni-ns#lecturer"/>
<uni:name>David Billington</uni:name><uni:title>Associate Professor</uni:title>
</rdf:Description>
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Abbreviated Syntax: Example
Original RDF:<rdf:Description rdf:ID="CIT1111">
<rdf:type rdf:resource="http://www.mydomain.org/uni-ns#course"/>
<uni:courseName>Discrete Maths</uni:courseName>
<uni:isTaughtBy rdf:resource="#949318"/></rdf:Description>
Simplified RDF:<uni:course rdf:ID="CIT1111" uni:courseName="Discrete
Maths"><uni:isTaughtBy rdf:resource="#949318"/>
</uni:course>
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Basic Ideas of RDF Schema
RDF is a universal language that lets users describe resources in their own vocabularies RDF does not assume, nor does it define
semantics of any particular application domain
The user can do so in RDF Schema using: Classes and Properties Class Hierarchies and Inheritance Property Hierarchies
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Class Hierarchies
Classes can be organised in hierarchies A is a subclass of B if every instance of A is
also an instance of B Then B is a superclass of A
A subclass graph need not be a tree A class may have multiple superclasses
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Property Hierarchies
Hierarchical relationships for properties E.g., “is taught by” is a subproperty of “involves” If a course C is taught by an academic staff member
A, then C also involves Α
The converse is not necessarily true E.g., A may be the teacher of the course C, or a tutor who marks student homework but does not
teach C
P is a subproperty of Q, if Q(x,y) is true whenever P(x,y) is true
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Example: A University
<rdfs:Class rdf:ID="lecturer"><rdfs:comment>
The class of lecturers. All lecturers are academic staff members.</rdfs:comment><rdfs:subClassOf rdf:resource="#academicStaffMember"/>
</rdfs:Class>
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Example: A University (2)
<rdfs:Class rdf:ID="course"><rdfs:comment>The class of courses</rdfs:comment>
</rdfs:Class>
<rdf:Property rdf:ID="isTaughtBy"><rdfs:comment>
Inherits its domain ("course") and range ("lecturer")
from its superproperty "involves"</rdfs:comment><rdfs:subPropertyOf rdf:resource="#involves"/>
</rdf:Property>
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Example: A University (3)<rdf:Property rdf:ID="involves">
<rdfs:comment> It relates only courses to lecturers. </rdfs:comment> <rdfs:domain rdf:resource="#course"/> <rdfs:range rdf:resource="#lecturer"/>
</rdf:Property>
<rdf:Property rdf:ID="phone"><rdfs:comment>
It is a property of staff membersand takes literals as values.
</rdfs:comment><rdfs:domain rdf:resource="#staffMember"/><rdfs:range rdf:resource=
"http://www.w3.org/2000/01/rdf-schema#Literal"/>
</rdf:Property>
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Semantics based on Inference Rules
Semantics in terms of RDF triples instead of restating RDF in terms of first-order logic
… and sound and complete inference systems This inference system consists of inference
rules of the form:IF E contains certain triplesTHEN add to E certain additional
triples where E is an arbitrary set of RDF triples
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Examples of Inference Rules
IF E contains the triple (?x,?p,?y)THEN E also contains (?p,rdf:type,rdf:property)
IF E contains the triples (?u,rdfs:subClassOf,?v) and (?v,rdfs:subclassOf,?w)
THEN E also contains the triple (?u,rdfs:subClassOf,?w)
IF E contains the triples (?x,rdf:type,?u) and (?u,rdfs:subClassOf,?v)
THEN E also contains the triple (?x,rdf:type,?v)
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Examples of Inference Rules (2)
Any resource ?y which appears as the value of a property ?p can be inferred to be a member of the range of ?p This shows that range definitions in RDF Schema are
not used to restrict the range of a property, but rather to infer the membership of the range
IF E contains the triples (?x,?p,?y) and (?p,rdfs:range,?u)
THEN E also contains the triple (?y,rdf:type,?u)
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Why an RDF Query Language?Different XML Representations
XML at a lower level of abstraction than RDF There are various ways of syntactically
representing an RDF statement in XML Thus we would require several XPath
queries, e.g. //uni:lecturer/uni:title if uni:title element //uni:lecturer/@uni:title if uni:title attribute Both XML representations equivalent!
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Example: Different XML for Same RDF
Original RDF:<rdf:Description rdf:ID="CIT1111">
<rdf:type rdf:resource="http://www.mydomain.org/uni-ns#course"/>
<uni:courseName>Discrete Maths</uni:courseName>
<uni:isTaughtBy rdf:resource="#949318"/></rdf:Description>
Application of First Simplification Rule:<rdf:Description rdf:ID="CIT1111"
uni:courseName="Discrete Maths"> <rdf:type rdf:resource=
"http://www.mydomain.org/uni-ns#course"/><uni:isTaughtBy rdf:resource="#949318"/>
</rdf:Description>
Application of 2nd Simplification Rule:<uni:course rdf:ID="CIT1111" uni:courseName="Discrete
Maths"><uni:isTaughtBy rdf:resource="#949318"/>
</uni:course>
SPARQL Basic Queries
SPARQL is based on matching graph patterns
The simplest graph pattern is the triple pattern: like an RDF triple, but with the possibility of a
variable instead of an RDF term in the subject, predicate, or object positions
Combining triple patterns gives a basic graph pattern, where an exact match to a graph is needed to fulfill a pattern
Examples
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>SELECT ?cWHERE{
?c rdf:type rdfs:Class .} Retrieves all triple patterns, where:
the property is rdf:type the object is rdfs:Class
Which means that it retrieves all classes
Examples (2) Get all instances of a particular class (e.g. course) :(declaration of rdf, rdfs prefixes omitted for brevity)
PREFIX uni: <http://www.mydomain.org/uni-ns#>SELECT ?iWHERE{
?i rdf:type uni:course .}
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Using select-from-where As in SQL, SPARQL queries have a SELECT-FROM-WHERE
structure: SELECT specifies the projection: the number and order of
retrieved data FROM is used to specify the source being queried
(optional) WHERE imposes constraints on possible solutions in the
form of graph pattern templates and boolean constraints Retrieve all phone numbers of staff members:
SELECT ?x ?yWHERE { ?x uni:phone ?y .}
Here ?x and ?y are variables, and ?x uni:phone ?y represents a resource-property-value triple pattern
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Implicit Join
Retrieve all lecturers and their phone numbers:
SELECT ?x ?yWHERE
{ ?x rdf:type uni:Lecturer ;
uni:phone ?y . }
Implicit join: We restrict the second pattern only to those triples, the resource of which is in the variable ?x Here we use a syntax shorcut as well: a semicolon indicates
that the following triple shares its subject with the previous one
Implicit join (2)
The previous query is equivalent to writing:
SELECT ?x ?yWHERE{
?x rdf:type uni:Lecturer .?x uni:phone ?y .
}
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Explicit Join
Retrieve the name of all courses taught by the lecturer with ID 949352
SELECT ?nWHERE{
?x rdf:type uni:Course ;uni:isTaughtBy :949352 .
?c uni:courseName ?n .FILTER (?c = ?x) .
}
Optional Patterns
<uni:lecturer rdf:about=“949352”><uni:name>Grigoris Antoniou</uni:name>
</uni:lecturer><uni:professor rdf:about=“94318”>
<uni:name>David Billington</uni:name><uni:email>david@work.example.org</uni:email>
</uni:professor>
For one lecturer it only lists the name For the other it also lists the email address
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Optional Patterns (2)
All lecturers and their email addresses:
SELECT ?name ?emailWHERE{?x rdf:type uni:Lecturer ;
uni:name ?name ;uni:email ?email .
}30
Optional Patterns (3)
The result of the previous query would be:
Grigoris Antoniou is listed as a lecturer, but he has no e-mail address
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?name ?email
David Billington david@work.example.org
Optional Patterns (4)
As a solution we can adapt the query to use an optional pattern:
SELECT ?name ?emailWHERE{?x rdf:type uni:Lecturer ;
uni:name ?name .OPTIONAL { x? uni:email ?
email }}
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Optional Patterns (5)
The meaning is roughly “give us the names of lecturers, and if known also their e-mail address”
The result looks like this:
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?name ?email
Grigoris Antoniou
David Billington david@work.example.org
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Summary
RDF provides a foundation for representing and processing metadata
RDF has a graph-based data model RDF has an XML-based syntax to support
syntactic interoperability XML and RDF complement each other because RDF
supports semantic interoperability RDF has a decentralized philosophy and allows
incremental building of knowledge, and its sharing and reuse
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Summary (2)
RDF is domain-independent - RDF Schema provides a mechanism for describing specific domains
RDF Schema is a primitive ontology language It offers certain modelling primitives with fixed
meaning Key concepts of RDF Schema are class,
subclass relations, property, subproperty relations, and domain and range restrictions
There exist query languages for RDF and RDFS, including SPARQL
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Expressive Power of RDF Schema
Classes and Sub-classes Properties and sub-properties Range and domain restriction on
properties Instances of classes
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Limitations of the Expressive Power of RDF Schema
Local scope of properties rdfs:range defines the range of a
property (e.g. eats) for all classes In RDF Schema we cannot declare
range restrictions that apply to some classes only
E.g. we cannot say that cows eat only plants, while other animals may eat meat, too
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Limitations of the Expressive Power of RDF Schema (2)
Disjointness of classes Sometimes we wish to say that classes
are disjoint (e.g. male and female) Boolean combinations of classes
Sometimes we wish to build new classes by combining other classes using union, intersection, and complement
E.g. person is the disjoint union of the classes male and female
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Limitations of the Expressive Power of RDF Schema (3)
Cardinality restrictions E.g. a person has exactly two parents, a
course is taught by at least one lecturer Special characteristics of properties
Transitive property (like “greater than”) Unique property (like “is mother of”) A property is the inverse of another
property (like “eats” and “is eaten by”)
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Requirements for Ontology Languages
Ontology languages allow users to write explicit, formal conceptualizations of domain models
The main requirements are: a well-defined syntax efficient reasoning support a formal semantics sufficient expressive power convenience of expression
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Tradeoff between Expressive Power and Efficient Reasoning Support
The richer the language is, the more inefficient the reasoning support becomes
Sometimes it crosses the border of noncomputability
We need a compromise: A language supported by reasonably
efficient reasoners A language that can express large classes
of ontologies and knowledge.
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Reasoning About Knowledge in Ontology Languages
Class membership If x is an instance of a class C, and C
is a subclass of D, then we can infer that x is an instance of D
Equivalence of classes If class A is equivalent to class B, and
class B is equivalent to class C, then A is equivalent to C, too
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Reasoning About Knowledge in Ontology Languages (2)
Consistency X instance of classes A and B, but A and B
are disjoint This is an indication of an error in the
ontology Classification
Certain property-value pairs are a sufficient condition for membership in a class A; if an individual x satisfies such conditions, we can conclude that x must be an instance of A
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Uses for Reasoning
Reasoning support is important for checking the consistency of the ontology and the
knowledge checking for unintended relationships between classes automatically classifying instances in classes
Checks like the preceding ones are valuable for designing large ontologies, where multiple authors are
involved integrating and sharing ontologies from various
sources
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Reasoning Support for OWL
Semantics is a prerequisite for reasoning support Formal semantics and reasoning support are
usually provided by mapping an ontology language to a known logical
formalism using automated reasoners that already exist for those
formalisms OWL is (partially) mapped on a description logic,
and makes use of reasoners such as FaCT and RACER
Description logics are a subset of predicate logic for which efficient reasoning support is possible
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Three Species of OWL
W3C’s Web Ontology Working Group defined OWL as three different sublanguages: OWL Full OWL DL OWL Lite
Each sublanguage geared toward fulfilling different aspects of requirements
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OWL Full
It uses all the OWL languages primitives It allows the combination of these
primitives in arbitrary ways with RDF and RDF Schema
OWL Full is fully upward-compatible with RDF, both syntactically and semantically
OWL Full is so powerful that it is undecidable No complete (or efficient) reasoning support
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OWL DL
OWL DL (Description Logic) is a sublanguage of OWL Full that restricts application of the constructors from OWL and RDF Application of OWL’s constructors’ to each other is
disallowed Therefore it corresponds to a well studied description
logic OWL DL permits efficient reasoning support But we lose full compatibility with RDF:
Not every RDF document is a legal OWL DL document. Every legal OWL DL document is a legal RDF
document.
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OWL Lite An even further restriction limits OWL DL
to a subset of the language constructors E.g., OWL Lite excludes enumerated classes,
disjointness statements, and arbitrary cardinality.
The advantage of this is a language that is easier to grasp, for users implement, for tool builders
The disadvantage is restricted expressivity
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OWL Compatibility with RDF Schema
All varieties of OWL use RDF for their syntax
Instances are declared as in RDF, using RDF descriptions
and typing informationOWL constructors are specialisations of theirRDF counterparts
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OWL XML/RDF Syntax: Header
<rdf:RDFxmlns:owl ="http://www.w3.org/2002/07/owl#"xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"xmlns:xsd ="http://www.w3.org/2001/ XLMSchema#">
An OWL ontology may start with a collection of assertions for housekeeping purposes using owl:Ontology element
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owl:Ontology
<owl:Ontology rdf:about=""><rdfs:comment>An example OWL ontology </rdfs:comment><owl:priorVersion
rdf:resource="http://www.mydomain.org/uni-ns-old"/><owl:imports
rdf:resource="http://www.mydomain.org/persons"/><rdfs:label>University Ontology</rdfs:label>
</owl:Ontology>
owl:imports is a transitive property
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Classes
Classes are defined using owl:Class owl:Class is a subclass of rdfs:Class
Disjointness is defined using owl:disjointWith
<owl:Class rdf:about="#associateProfessor"><owl:disjointWith rdf:resource="#professor"/><owl:disjointWith rdf:resource="#assistantProfessor"/>
</owl:Class>
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Classes (2)
owl:equivalentClass defines equivalence of classes
<owl:Class rdf:ID="faculty"><owl:equivalentClass rdf:resource= "#academicStaffMember"/>
</owl:Class>
owl:Thing is the most general class, which contains everything
owl:Nothing is the empty class
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Properties
In OWL there are two kinds of properties Object properties, which relate
objects to other objects•E.g. is-TaughtBy, supervises
Data type properties, which relate objects to datatype values•E.g. phone, title, age, etc.
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Datatype Properties
OWL makes use of XML Schema data types, using the layered architecture of the Semantic Web
<owl:DatatypeProperty rdf:ID="age"><rdfs:range rdf:resource= "http://www.w3.org/2001/XLMSchema
#nonNegativeInteger"/></owl:DatatypeProperty>
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Object Properties
User-defined data types
<owl:ObjectProperty rdf:ID="isTaughtBy"><owl:domain rdf:resource="#course"/><owl:range rdf:resource= "#academicStaffMember"/><rdfs:subPropertyOf rdf:resource="#involves"/>
</owl:ObjectProperty>
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Inverse Properties
<owl:ObjectProperty rdf:ID="teaches"><rdfs:range rdf:resource="#course"/><rdfs:domain rdf:resource= "#academicStaffMember"/><owl:inverseOf rdf:resource="#isTaughtBy"/>
</owl:ObjectProperty>
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Equivalent Properties
owl:equivalentProperty<owl:ObjectProperty rdf:ID="lecturesIn"><owl:equivalentProperty rdf:resource="#teaches"/>
</owl:ObjectProperty>
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Property Restrictions
In OWL we can declare that the class C satisfies certain conditions All instances of C satisfy the conditions
This is equivalent to saying that C is subclass of a class C', where C' collects all objects that satisfy the conditions C' can remain anonymous
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Property Restrictions (2)
A (restriction) class is achieved through an owl:Restriction element
This element contains an owl:onProperty element and one or more restriction declarations
One type defines cardinality restrictions (at least one, at most 3,…)
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Property Restrictions (3)
The other type defines restrictions on the kinds of values the property may take owl:allValuesFrom specifies
universal quantification owl:hasValue specifies a specific
value owl:someValuesFrom specifies
existential quantification
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owl:allValuesFrom
<owl:Class rdf:about="#firstYearCourse"><rdfs:subClassOf> <owl:Restriction>
<owl:onProperty rdf:resource="#isTaughtBy"/>
<owl:allValuesFrom rdf:resource="#Professor"/> </owl:Restriction></rdfs:subClassOf>
</owl:Class>
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owl:hasValue
<owl:Class rdf:about="#mathCourse"><rdfs:subClassOf>
<owl:Restriction><owl:onProperty rdf:resource=
"#isTaughtBy"/><owl:hasValue rdf:resource=
"#949352"/></owl:Restriction>
</rdfs:subClassOf></owl:Class>
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owl:someValuesFrom
<owl:Class rdf:about="#academicStaffMember"><rdfs:subClassOf> <owl:Restriction>
<owl:onProperty rdf:resource="#teaches"/>
<owl:someValuesFrom rdf:resource=
"#undergraduateCourse"/> </owl:Restriction></rdfs:subClassOf>
</owl:Class>
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Cardinality Restrictions
We can specify minimum and maximum number using owl:minCardinality and owl:maxCardinality
It is possible to specify a precise number by using the same minimum and maximum number
For convenience, OWL offers also owl:cardinality
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Cardinality Restrictions (2)
<owl:Class rdf:about="#course"><rdfs:subClassOf>
<owl:Restriction><owl:onProperty
rdf:resource="#isTaughtBy"/><owl:minCardinality rdf:datatype=
"&xsd;nonNegativeInteger">1</owl:minCardinality>
</owl:Restriction></rdfs:subClassOf>
</owl:Class>
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Special Properties
owl:TransitiveProperty (transitive property) E.g. “has better grade than”, “is ancestor of”
owl:SymmetricProperty (symmetry) E.g. “has same grade as”, “is sibling of”
owl:FunctionalProperty defines a property that has at most one value for each object E.g. “age”, “height”, “directSupervisor”
owl:InverseFunctionalProperty defines a property for which two different objects cannot have the same value
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Special Properties (2)
<owl:ObjectProperty rdf:ID="hasSameGradeAs">
<rdf:type rdf:resource="&owl;TransitiveProperty"/>
<rdf:type rdf:resource="&owl;SymmetricProperty"/>
<rdfs:domain rdf:resource="#student"/>
<rdfs:range rdf:resource="#student"/>
</owl:ObjectProperty>
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Boolean Combinations We can combine classes using Boolean
operations (union, intersection, complement)
<owl:Class rdf:about="#course"><rdfs:subClassOf>
<owl:Restriction><owl:complementOf
rdf:resource= "#staffMember"/>
</owl:Restriction></rdfs:subClassOf>
</owl:Class>
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Boolean Combinations (2)
<owl:Class rdf:ID="peopleAtUni"><owl:unionOf rdf:parseType="Collection">
<owl:Class rdf:about="#staffMember"/>
<owl:Class rdf:about="#student"/></owl:unionOf>
</owl:Class>
The new class is not a subclass of the union, but rather equal to the union We have stated an equivalence of classes
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Boolean Combinations (3)
<owl:Class rdf:ID="facultyInCS"><owl:intersectionOf rdf:parseType="Collection">
<owl:Class rdf:about="#faculty"/><owl:Restriction>
<owl:onProperty rdf:resource="#belongsTo"/>
<owl:hasValue rdf:resource= "#CSDepartment"/>
</owl:Restriction></owl:intersectionOf>
</owl:Class>
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Nesting of Boolean Operators
<owl:Class rdf:ID="adminStaff"><owl:intersectionOf rdf:parseType="Collection">
<owl:Class rdf:about="#staffMember"/><owl: Class> <owl:complementOf> <owl: Class>
<owl:unionOf rdf:parseType="Collection">
<owl:Class rdf:about="#faculty"/> <owl:Class
rdf:about=#techSupportStaff"/> </owl:unionOf>
</owl: Class> </owl:complementOf>
</owl: Class> </owl:intersectionOf></owl:Class>
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Enumerations with owl:oneOf
<owl:Class rdf:ID="weekdays"><owl:oneOf rdf:parseType="Collection">
<owl:Thing rdf:about="#Monday"/><owl:Thing rdf:about="#Tuesday"/><owl:Thing rdf:about="#Wednesday"/><owl:Thing rdf:about="#Thursday"/><owl:Thing rdf:about="#Friday"/><owl:Thing rdf:about="#Saturday"/><owl:Thing rdf:about="#Sunday"/>
</owl:oneOf></owl:Class>
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Declaring Instances
Instances of classes are declared as in RDF:
<rdf:Description rdf:ID="949352"><rdf:type rdf:resource= "#academicStaffMember"/>
</rdf:Description><academicStaffMember rdf:ID="949352">
<uni:age rdf:datatype="&xsd;integer"> 39<uni:age>
</academicStaffMember>
79
No Unique-Names Assumption
OWL does not adopt the unique-names assumption of database systems If two instances have a different name or ID
does not imply that they are different individuals
Suppose we state that each course is taught by at most one staff member, and that a given course is taught by two staff members An OWL reasoner does not flag an error Instead it infers that the two resources are
equal
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Distinct Objects
To ensure that different individuals are indeed recognized as such, we must explicitly assert their inequality:
<lecturer rdf:about="949318"><owl:differentFrom rdf:resource="949352"/>
</lecturer>
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Distinct Objects (2)
OWL provides a shorthand notation to assert the pairwise inequality of all individuals in a given list
<owl:allDifferent><owl:distinctMembers rdf:parseType="Collection">
<lecturer rdf:about="949318"/><lecturer rdf:about="949352"/><lecturer rdf:about="949111"/>
</owl:distinctMembers></owl:allDifferent>
82
Data Types in OWL
XML Schema provides a mechanism to construct user-defined data types E.g., the data type of adultAge includes all integers
greater than 18
Such derived data types cannot be used in OWL The OWL reference document lists all the XML
Schema data types that can be used These include the most frequently used types such
as string, integer, Boolean, time, and date.
83
Combination of Features
In different OWL languages there are different sets of restrictions regarding the application of features
In OWL Full, all the language constructors may be used in any combination as long as the result is legal RDF
84
Restriction of Features in OWL DL
Vocabulary partitioning Any resource is allowed to be only a class,
a data type, a data type property, an object property, an individual, a data value, or part of the built-in vocabulary, and not more than one of these
Explicit typing The partitioning of all resources must be
stated explicitly (e.g. a class must be declared if used in conjunction with rdfs:subClassOf)
85
Restriction of Features in OWL DL (2)
Property Separation The set of object properties and data
type properties are disjoint Therefore the following can never be
specified for data type properties:owl:inverseOfowl:FunctionalPropertyowl:InverseFunctionalProperty
owl:SymmetricProperty
86
Restriction of Features in OWL DL (3)
No transitive cardinality restrictions No cardinality restrictions may be placed
on transitive properties Restricted anonymous classes:
Anonymous classes are only allowed to occur as: the domain and range of either
owl:equivalentClass or owl:disjointWith
the range (but not the domain) of rdfs:subClassOf
87
Restriction of Features in OWL Lite
Restrictions of OWL DL and more owl:oneOf, owl:disjointWith, owl:unionOf,
owl:complementOf and owl:hasValue are not allowed
Cardinality statements (minimal, maximal, and exact cardinality) can only be made on the values 0 or 1
owl:equivalentClass statements can no longer be made between anonymous classes but only between class identifiers
91
An African Wildlife Ontology – Properties
<owl:TransitiveProperty rdf:ID="is-part-of"/>
<owl:ObjectProperty rdf:ID="eats"><rdfs:domain rdf:resource="#animal"/>
</owl:ObjectProperty>
<owl:ObjectProperty rdf:ID="eaten-by"><owl:inverseOf rdf:resource="#eats"/>
</owl:ObjectProperty>
92
An African Wildlife Ontology – Plants and Trees
<owl:Class rdf:ID="plant"><rdfs:comment>Plants form a class disjoint from animals. </rdfs:comment><owl:disjointWith rdf:resource="#animal"/>
</owl:Class>
<owl:Class rdf:ID="tree"><rdfs:comment>Trees are a type of plant. </rdfs:comment><rdfs:subClassOf rdf:resource="#plant"/>
</owl:Class>
93
An African Wildlife Ontology – Branches
<owl:Class rdf:ID="branch"><rdfs:comment>Branches are parts of trees. </rdfs:comment><rdfs:subClassOf>
<owl:Restriction><owl:onProperty rdf:resource="#is-
part-of"/><owl:allValuesFrom
rdf:resource="#tree"/></owl:Restriction>
</rdfs:subClassOf></owl:Class>
94
An African Wildlife Ontology – Leaves
<owl:Class rdf:ID="leaf"><rdfs:comment>Leaves are parts of branches. </rdfs:comment><rdfs:subClassOf>
<owl:Restriction><owl:onProperty rdf:resource="#is-
part-of"/><owl:allValuesFrom
rdf:resource="#branch"/></owl:Restriction>
</rdfs:subClassOf></owl:Class>
95
An African Wildlife Ontology – Carnivores
<owl:Class rdf:ID="carnivore"><rdfs:comment>Carnivores are exactly those animalsthat eat animals.</rdfs:comment><owl:intersectionOf rdf:parsetype="Collection"><owl:Class rdf:about="#animal"/>
<owl:Restriction><owl:onProperty rdf:resource="#eats"/><owl:someValuesFrom
rdf:resource="#animal"/></owl:Restriction>
</owl:intersectionOf></owl:Class>
96
An African Wildlife Ontology – Giraffes
<owl:Class rdf:ID="giraffe"><rdfs:comment>Giraffes are herbivores, and theyeat only leaves.</rdfs:comment><rdfs:subClassOf rdf:type="#herbivore"/><rdfs:subClassOf>
<owl:Restriction><owl:onProperty rdf:resource="#eats"/><owl:allValuesFrom
rdf:resource="#leaf"/></owl:Restriction>
</rdfs:subClassOf></owl:Class>
97
An African Wildlife Ontology – Lions
<owl:Class rdf:ID="lion"><rdfs:comment>Lions are animals that eatonly herbivores.</rdfs:comment><rdfs:subClassOf rdf:type="#carnivore"/><rdfs:subClassOf>
<owl:Restriction><owl:onProperty
rdf:resource="#eats"/><owl:allValuesFrom
rdf:resource="#herbivore"/></owl:Restriction>
</rdfs:subClassOf></owl:Class>
98
Summary
OWL is the proposed standard for Web ontologies
OWL builds upon RDF and RDF Schema: (XML-based) RDF syntax is used Instances are defined using RDF
descriptions Most RDFS modeling primitives are
used
99
Summary (2)
Formal semantics and reasoning support is provided through the mapping of OWL on logics Predicate logic and description logics have
been used for this purpose While OWL is sufficiently rich to be used
in practice, extensions are in the making They will provide further logical features,
including rules
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