Ontology modelling and the semantic web Asgeir Rekkavik Deichmanske bibliotek

Librarian / consultant at Deichmanske bibliotek (Oslo Public Library) ...since 2004. Involved in ontology related projects since 2006 Los topic structure for indexing public services Sublima tool for subject driven portals Mediazone multimediastations

Librarian / consultant at Deichmanske bibliotek (Oslo Public Library)

...since 2004.

Involved in ontology related projects since 2006

Los topic structure for indexing public services

Sublima tool for subject driven portals

Mediazone multimediastations

What does semantic mean? Semantics : The branch of linguistics concerned with meaning. ( Shorter Oxford English dictionary ) Semantics is the study of meaning, usually in language. (Wikipedia 2009-10-19)

Semantics : The branch of linguistics concerned with meaning.

( Shorter Oxford English dictionary )

Semantics is the study of meaning, usually in language.

(Wikipedia 2009-10-19)

I love you I ♥ U Different syntax, same semantics

I love you

I ♥ U

Different syntax, same semantics

What does ontology mean? Ontology : The science or study of being. ( Shorter Oxford English dictionary) In computer science and information science, an ontology is a formal representation of a set of concepts within a domain and the relationships between those concepts. (Wikipedia 2009-10-19)

Ontology : The science or study of being.

( Shorter Oxford English dictionary)

In computer science and information science, an ontology is a formal representation of a set of concepts within a domain and the relationships between those concepts.

(Wikipedia 2009-10-19)

What does ontology mean? The world can be described in many different ways: e.g. language, art etc. An ontology describes the world in a way that is formal, structured and unambiguous. Why? Because we want to describe it to computers.

The world can be described in many different ways: e.g. language, art etc.

An ontology describes the world in a way that is formal, structured and unambiguous.

Why? Because we want to describe it to computers.

Taxonomies Hierarchical classification Characteristics Generic relations (’is-a’ relations) Directed graph Nodes represent categories Arrows represent broader/narrower relations Especially known from biology. Developed by Carl von Linné.

Hierarchical classification

Characteristics

Generic relations (’is-a’ relations)

Directed graph

Nodes represent categories

Arrows represent broader/narrower relations

Especially known from biology. Developed by Carl von Linné.

Taxonomies

Taxonomies Other transitive relations can exist between concepts, e.g. ’part-of’ relations

Other transitive relations can exist between concepts, e.g. ’part-of’ relations

Different types of relations Generic (”is-a”, e.g. Cat - Animal) Partitive (’part-of’, e.g. Oslo - Norway) Instance (e.g. Sokrates - Philospher) Associative (several) In a thesaurus, the generic, partitive and instance relations are all expressed as broader / narrower. No distinction between different associative relations.

Generic (”is-a”, e.g. Cat - Animal)

Partitive (’part-of’, e.g. Oslo - Norway)

Instance (e.g. Sokrates - Philospher)

Associative (several)

In a thesaurus, the generic, partitive and instance relations are all expressed as broader / narrower. No distinction between different associative relations.

Thesaurus hierarchy

Generic class hierarchy

Generic class hierarchy

Prot égé Free, open source ontology editor Developed by Stanford University and the University of Manchester Latest version Prot égé 4.0 Available from: http://protege.stanford.edu Currently developing: WebProt égé (Alpha)

Free, open source ontology editor

Developed by Stanford University and the University of Manchester

Latest version Prot égé 4.0

Available from:

http://protege.stanford.edu

Currently developing: WebProt égé (Alpha)

Classes Represent categories, sets of individual instances Are related to eachother through parent-child relationships (superclass-subclass) Only generic ’is a’ -relations are allowed Unlike in a taxonomy, multiple inheritence is allowed.

Represent categories, sets of individual instances

Are related to eachother through parent-child relationships (superclass-subclass)

Only generic ’is a’ -relations are allowed

Unlike in a taxonomy, multiple inheritence is allowed.

Properties of classes Classes can be: Disjoint (if n is a member of A, n is not a member of B) (e.g. if Robin is a girl, then Robin is not a boy) Equivalent (if n is a member of A, n is also a member of B) (e.g. Firstgraders  Pupils born in 2003)

Classes can be:

Disjoint

(if n is a member of A, n is not a member of B)

(e.g. if Robin is a girl, then Robin is not a boy)

Equivalent

(if n is a member of A, n is also a member of B)

(e.g. Firstgraders  Pupils born in 2003)

Exercise Create a taxonomy with these classes: Bicycle Boat Bulldog Car Cat Colour Dog Dolphin Flower Man Oak Person Pet Pinetree Plant Puppy Rose Whale Woman Zebra

Bicycle

Boat

Bulldog

Car

Cat

Colour

Dog

Dolphin

Flower

Man

Oak

Person

Pet

Pinetree

Plant

Puppy

Rose

Whale

Woman

Zebra

Instances Individual entities that can populate any number of classes. An instance that is a member of a class, is necessarily also a member of all its superclasses.

Individual entities that can populate any number of classes.

An instance that is a member of a class, is necessarily also a member of all its superclasses.

Exercise Create these instances:

The semantic triple A semantic triple is a statement consisting of three parts: an instance a property that refers to that instance a value for that property George likes chocolate

A semantic triple is a statement consisting of three parts:

an instance

a property that refers to that instance

a value for that property

George likes chocolate

Properties The instances are described through properties . There are two different types of properties: Object property: Takes another instance as value e.g. Alice knows Fred Datatype property Takes a distinct value, like a number, a string etc. e.g. King Harald has year of birth 1937 The property is the ”predicate” in the semantic triple.

The instances are described through properties .

There are two different types of properties:

Object property:

Takes another instance as value

e.g. Alice knows Fred

Datatype property

Takes a distinct value, like a number, a string etc.

e.g. King Harald has year of birth 1937

The property is the ”predicate” in the semantic triple.

Properties of properties Properties can be: symmetric (Martin has cousin Thomas)  (Thomas has cousin Martin) asymmetric (Martin is father of Rosie)  (Rosie can not be father of Martin) inverse (Martin is parent of Rosie) (Rosie is child of Martin) transitive (Rosie descends from Martin) and (Martin descends from Emma)  (Rosie descends from Emma) functional (can have only one value) inverse functional (value can be held by only one instance)

Properties can be:

symmetric

(Martin has cousin Thomas)  (Thomas has cousin Martin)

asymmetric

(Martin is father of Rosie)  (Rosie can not be father of Martin)

inverse

(Martin is parent of Rosie) (Rosie is child of Martin)

transitive

(Rosie descends from Martin) and (Martin descends from Emma)

 (Rosie descends from Emma)

functional (can have only one value)

inverse functional (value can be held by only one instance)

Domain and Range The domain and range of a property determine what kind of instances it can be used for and what kind of values it can have. Domain The class, whose instances can have the property If domain is not set, domain=Thing Range The class, whose instances can be value for an object property The type of data that is allowed as value for a datatype property

The domain and range of a property determine what kind of instances it can be used for and what kind of values it can have.

Domain

The class, whose instances can have the property

If domain is not set, domain=Thing

Range

The class, whose instances can be value for an object property

The type of data that is allowed as value for a datatype property

Exercise Object properties Create the following object properties owns hasOwner hasNeigbour Set domain and range correctly Connect instances, so that: Mr. Taylor owns Duchess Mrs. Robertson owns Lassie Mr. Taylor and Mrs. Robertson are neighbours

Create the following object properties

owns

hasOwner

hasNeigbour

Set domain and range correctly

Connect instances, so that:

Mr. Taylor owns Duchess

Mrs. Robertson owns Lassie

Mr. Taylor and Mrs. Robertson are neighbours

Restrictions Classes can be populated according to rules called restrictions. This is done by expressing that a class is equivalent to a certain set of instances. The set can be defined by combining other classes with and/or/not operators using criteria based on desired properties for the instances

Classes can be populated according to rules called restrictions.

This is done by expressing that a class is equivalent to a certain set of instances.

The set can be defined by

combining other classes with and/or/not operators

using criteria based on desired properties for the instances

Examples of restrictions LivingThing  Animal or Plant or Person Property  hasOwner some Person Pet  Animal and (hasOwner some Person)

LivingThing  Animal or Plant or Person

Property  hasOwner some Person

Pet  Animal and (hasOwner some Person)

Exercise Person-Place ontology Create a class hierarchy to describe persons by gender and function e.g. Man, Woman, Author, Actor, Artist, Composer, Scientist, Biologist, Astronomer, Politician etc. Create classes to describe different kinds of regions e.g. Continent, Country, City etc. Create object properties isFrom-property (person-region) partOf-property (region-region) Create instances of both types, relate them with suitable properties Use restrictions to create new classes, such as: FemaleAuthor (Woman and Author) SwedishPersons (Person and isFrom value Sweden)

Create a class hierarchy to describe persons by gender and function

e.g. Man, Woman, Author, Actor, Artist, Composer, Scientist, Biologist, Astronomer, Politician etc.

Create classes to describe different kinds of regions

e.g. Continent, Country, City etc.

Create object properties

isFrom-property (person-region)

partOf-property (region-region)

Create instances of both types, relate them with suitable properties

Use restrictions to create new classes, such as:

FemaleAuthor (Woman and Author)

SwedishPersons (Person and isFrom value Sweden)