owl 2 web ontology language. topics introduction to owl usage of owl problems with owl 1 solutions...
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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 membersQCR 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 ExpressivityBritish citizen must have a passport number which is an xsd: stringWe 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 RestrictionsQCR 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
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.