owl 2 web ontology language. topics introduction to owl usage of owl problems with owl 1 solutions...

OWL 2Web Ontology Language

TopicsIntroduction to OWL

Usage of OWL

Problems with OWL 1

Solutions from OWL 2

OWL IntroductionInitially focus was on RDF and RDF SchemaOWL is a family of three language variants 1. OWL Lite 2. OWL DL 3. OWL FullOWL is a standardized language.

Usage of OWLOWL Ontologies are used in areas such as e-

Science, medicine, biology, geography, astronomy, defense, automotive and aerospace industries.

OWL is extensively used in life sciences community.

Problems in OWL 1Expressivity IssuesProblems with syntaxDeficiencies in the definition

Expressivity LimitationsLacks several constructsCommunity users introduced various patternsStill IncompleteProblem with 1) Qualified Cardinality Restriction 2) Relational Expressivity 3) Data type Expressivity 4) Keys

1) Qualified Cardinality Restriction(QCR)Ex: “Persons that have at least one child who is

male” ---existential restriction (qualified)Ex: “Person with at least 3 children who are

male”---cardinality restriction(not qualified)Some situations where QCR is used i) Define a quadruped animal with exactly 4 parts

that are legs. ii) Medical Committee consisting of at least 5

members, 2 are medically qualified, 1 is manager and 2 are public members

QCR was used in DAML + OIL---predecessor of OWL

2)Relational ExpressivityPropagation along properties Ex: “Abnormality of a part of an anatomical

structure constitutes an abnormality of the structure as a whole”.

Properties of Properties Ex: “If x is part of y and y is part of z then x

is part of z” reflexive(every object is a part of itself)

asymmetric (nothing is a part of one of its parts).

Data type Expressivity“British citizen must have a passport number

which is an xsd: string”We cannot express 1) restrictions to a subset of datatype values 2) relationships between values of data

properties on one object 3) relationships between values of data

properties on different objects 4)aggregate functions

4) KeysOWL DL does not support Key Constraints on

data properties. Ex: “US Citizens are uniquely identified by

their SSN” This is not possibleOWL Full supports this using inverse

functional properties.

2) Syntax IssuesOWL 1 uses 2 types of syntax 1. Abstract Syntax 2. OWL 1 RDF

Both are difficult to parse.

1) Frame-Based ParadigmAxiom Ex: “Tiger is a Class and it is a subclass of

Class Cat” Class(Tiger partial Cat) “Class Tiger is a subclass of Class Predator” Adding, SubClassOf(Tiger Predator)

Ans: Cat and Predator

2) Alignment with DL ConstructsDL allows only one class to appear in property

restriction Ex: restriction( hasParent SomeValuesFrom(Person) allValuesFrom(Person)) This can be translated into intersectionOf( restriction(hasParent SomeValuesFrom(Person)) restriction(hasParent allValuesFrom(Person))

3) Types of Ontology EntitiesEx: class(Person partial restriction(hasMother SomeValuesFrom(Woman))

Ex: DisjointClasses(Animal Plant) SubClassOf(Human Animla)

4) Problems with OWL 1 RDFInformation is represented in triplesEx: A is UNION of B and C (A, owl:unionOf, _:x1) (_:x1, rdf:first, B) (_:x1, rdf:rest, _:x2) (_:x2, rdf:first, C) (_:x2, rdf:rest, rdf:nil) This is difficult to read

MetamodelingEx: “Harry is an Eagle” “Eagles are endangered species”

--Individual Harry is an instance of Class Eagle--Individual Eagle id an instance of Class

Endangered Species.Eagle is Individual in one and Class in the

another.

Imports and VersioningImports one ontology from anotherURI must point to the location of imported

ontology and the location should match with the name of imported ontology.

Coupling of names and location is not possible when ontologies are moved.

Solutions from OWL 21)Qualified Number Restrictions

QCR is implemented in OWL 2

2) Relational ExpressivityAddressed using Complex Property Inclusion Axioms Ex: “If a contains b and b has a part c, then a also contains

c” subPropertyOf( Propertychain(contains hasPart) contains) Ex: “If b is part of a and b contains c , then c is also a part

of a” subProperty( Propertychain(hasPart hasPart) hasPart)---Cycle of dependency between contains and hasPart

OWL 2 supports transitive, reflexive and asymmetric.

3) Increasing Data type ExpressivityOWL 2 supports owl:boolean, owl:string,

xsd:integer, xsd:dateTime, xsd:hexBinary

Build new data types by providing data type restriction construct.

Ex: DatatypeRestriction(xsd:integer xsd:minInclusive 18)

4) KeysOWL 2 implements Easy Keys.Key Axioms are of the form HashKey(C P1,……Pn) This states that object or data type

properties Pi are keys for instance of Class C.No two instances of C can coincide on values

of Pi. Ex: HashKey(Person hasSSN)

2 assertions can be made PropertyAssertion(PSmith hasSSN “123-45-

6789”) PropertyAssertion(PeterSmith hasSSN “123-

45-6789”)---Psmith and PeterSmith are same individuals.Easy Keys are not applied to individuals not

known by name Ex: Jane is connected through marriedTo to

an individual x that is an instance of Man and that has “123-45-6789” as the value of hasSSN.

ClassAssertion( SomeValuesFrom(marriedTo IntersectionOf( Man HasValue(hasSSN “123-45-6789”))) Jane)

--We cannot conclude that

ClassAssertion(Man Psmith)

MOF MetamodelIt is a meta language and used for specifying

other languages.It is also a Structural Specification presented

using UML.

Typing and DeclarationsEx: Declaration(Class(Plant)) Declaration(Class(Animal))

SubPropertyOf(P Q) Both P and Q must be declared, otherwise we

cannot conclude whether they are objects or data type properties.

Metamodeling with Punning Ex: “Eagles are endangered species” “Harry is an Eagle”

------ClassAssertion(Eagle Harry) ClassAssertion(Endangered Eagle)This can be interpreted in OWL 2 as ClassAssertion(Class-Eagle Individual-Harry) ClassAssertion(Class-Endangered Individual-

Eagle)---This type of meta modeling is referred as Punning.

Annotation of Axiom Ex: “Humans are animals and attributes that

statement to Peter” SubClassOf( Annotation(attributedTo “Peter”) Human Animal)---Annotations do not affect the semantics of

ontology but they do affect the structural equivalence.

SubClassOf(Human Animal) This is semantically equivalent to the

above onebut not structurally.

Imports and VersioningOWL 2 allows redirection mechanism.OWL 2 contains Version URI which identifies

the version of the ontology.

ConclusionApart from addressing problems in OWL 1,

goal of OWL 2 is to provide a robust platform for future development.

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