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AMRUTA PRIYA MOGILINEEDI apm075000@utdallas.edu. OWL 2 Web Ontology Language. Topics. Introduction to OWL Usage of OWL Problems with OWL 1 Solutions from OWL 2. OWL Introduction.

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owl 2 web ontology language

AMRUTA PRIYA MOGILINEEDI apm075000@utdallas.edu

OWL 2

Web Ontology Language

topics
Topics
  • Introduction to OWL
  • Usage of OWL
  • Problems with OWL 1
  • Solutions from OWL 2
owl introduction
OWL Introduction
  • Initially focus was on RDF and RDF Schema
  • OWL is a family of three language variants

1. OWL Lite

2. OWL DL

3. OWL Full

  • OWL is a standardized language.
usage of owl
Usage of OWL
  • OWL 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 1
Problems in OWL 1
  • Expressivity Issues
  • Problems with syntax
  • Deficiencies in the definition
expressivity limitations
Expressivity Limitations
  • Lacks several constructs
  • Community users introduced various patterns
  • Still Incomplete
  • Problem with

1) Qualified Cardinality Restriction

2) Relational Expressivity

3) Data type Expressivity

4) Keys

1 qualified cardinality restriction qcr
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 expressivity
2)Relational Expressivity
  • Propagation 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
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 keys
4) Keys
  • OWL DL does not support Key Constraints on data properties.

Ex: “US Citizens are uniquely identified by their SSN”

This is not possible

  • OWL Full supports this using inverse functional properties.
2 syntax issues
2) Syntax Issues
  • OWL 1 uses 2 types of syntax

1. Abstract Syntax

2. OWL 1 RDF

  • Both are difficult to parse.
1 frame based paradigm
1) Frame-Based Paradigm
  • Axiom

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 constructs
2) Alignment with DL Constructs
  • DL 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 entities
3) Types of Ontology Entities
  • Ex: class(Person partial

restriction(hasMother

SomeValuesFrom(Woman))

  • Ex:

DisjointClasses(Animal Plant)

SubClassOf(Human Animla)

4 problems with owl 1 rdf
4) Problems with OWL 1 RDF
  • Information is represented in triples
  • Ex: 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

metamodeling
Metamodeling
  • Ex: “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 versioning
Imports and Versioning
  • Imports one ontology from another
  • URI 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.
2 relational expressivity1
2) Relational Expressivity
  • Addressed 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(hasParthasPart)

hasPart)

---Cycle of dependency between contains and hasPart

  • OWL 2 supports transitive, reflexive and asymmetric.
3 increasing data type expressivity
3) Increasing Data type Expressivity
  • OWL 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 keys1
4) Keys
  • OWL 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)

slide22

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.

slide23

ClassAssertion(

SomeValuesFrom(marriedTo

IntersectionOf(

Man

HasValue(hasSSN “123-45-6789”)))

Jane)

--We cannot conclude that

ClassAssertion(Man Psmith)

mof metamodel
MOF Metamodel
  • It is a meta language and used for specifying other languages.
  • It is also a Structural Specification presented using UML.
typing and declarations
Typing and Declarations
  • Ex: 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
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
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 one

but not structurally.

imports and versioning1
Imports and Versioning
  • OWL 2 allows redirection mechanism.
  • OWL 2 contains Version URI which identifies the version of the ontology.
conclusion
Conclusion
  • Apart from addressing problems in OWL 1, goal of OWL 2 is to provide a robust platform for future development.