Ontologies: vehicles for reuse

Ontologies:vehicles for reuse

Course “Knowledge & Media”September 2015

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Overview• The notion of ontology• Common ontologies• Example ontology engineering topic:

– Part-whole relations

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The notion of ontology

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Concepts

• Help us organize the world around us• Act as recognition device• Test for reality• We use many different types of concepts

Concept types

Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

The concept triad

Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

Concept specification• Symbol

– Name used for the concept– Can be different names, different languages– E.g., “bike”, fiets”

• Intension (definition)– Intended meaning of the concept (semantics)– E.g. a bike has at least one wheel and a human-

powered movement mechanism• Extension

– Set of examples of the concept– E.g. “my bike”, “your bike”

Incomplete concept specifications

• Are common• Think of an example:

– Concept with no instances– Concept with no symbol

• Primitive vs. defined concepts

What is an Ontology?• In philosophy: theory of what exists in the world

• In IT: consensual & formal description of shared concepts in a domain• Aid to human communication and shared

understanding, by specifying meaning• Machine-processable (e.g., agents use ontologies in

communication)• Key technology in semantic information processing• Applications: knowledge management, e-business,

semantic world-wide web.

What is an Ontology?

“explicit specification of a shared conceptualization that holds in a particular

context” (Gruber’s definition in extended form)

Ontology spectrum

Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

Domain = area of interest

• Can be any size – e.g., medicine

• Concepts may have different symbols in different domains

• The same symbol may be used for different concepts in different domains (sometimes also in the same domain)

Context and DomainPrinciple 1: “The representation of real-world objects always depends

on the context in which the object is used. This context can be seen as a “viewpoint” taken on the object. It is usually impossible to enumerate in advance all the possible useful viewpoints on (a class of ) objects.”

Principle 2: “Reuse of some piece of information requires an explicit

description of the viewpoints that are inherently present in the information. Otherwise, there is no way of knowing whether, and why this piece of information is applicable in a new application setting.”

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Top-level categories:many different proposals

Chandrasekaran et al. (1999)

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The is-a hierarchy

Classes as instances

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Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

Categorization• Logic (and essentially also databases)

take an “extensional” view of classes– A class is a set and is completely defined by

the set members• This puts the emphasis on specifying class

boundaries• Work of Rosch et al. takes a different view

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Categories (Rosch)• Help us to organize the world• Tools for perception• Basic-level categories

– Are the prime categories used by people– Have the highest number of common and

distinctive attributes– What those basic-level categories are may

depend on context

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Basic-level categories

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Vertical organization of hierarchies• Basic-level classes often occur as a

middle layer in hierarchies• Higher levels: abstract classes that

organize the hierarchy• Lower levels: domain/context specific

classes– may require particular expertise to understand

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Class room exercise• Consider what needs to be included in a

mini ontology for representing people with their gender, length and blood pressure values. – Think also of geographical and cultural issues– Directly relevant for the design of an

Electronic Patient Record!

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COMMON ONTOLOGIES

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Friend of a Friend (FOAF)• Describing people:

– names– depictions– friends, acquaintances, relations– organizations– e-mail addresses– webpages– ...

• see http://xmlns.com/foaf/spec/

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Agents: People and Groups

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Agent identity• When are two Agents the same?

– definitely when they have the same URI or openID– probably when they have the same e-mail address... – maybe when they have the same name...

William of Orange (William the Silent? William III of England?)

• Disambiguation is an important task on the Web

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Dublin Core• A basic schema to improve resource

discovery on the web, i.e. finding stuff.• Consists of 15 basic elements that are all

optional, extensible, and repeatable.• International and interdisciplinary.• see http://purl.org/dc/• Newest version: 1.1

http://dublincore.org/documents/dces/

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Dublin Core 1.0 Elements– Title– Creator– Subject– Description– Publisher– Contributor– Date– Type

– Format– Identifier– Source– Language– Relation– Coverage– Rights

Time ontology• Time point versus time interval

– View point as special case of an interval with identical start and end

• Representation of time and duration concepts

• Seehttp://www.w3.org/TR/owl-time/

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Allen’s time relations

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PART-WHOLE RELATIONS

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Part-whole relations• “Mereology” = theory of part-whole

– “meros” is Greek for part• Common in many domains

– Human body, cars, installations, documents• Different from the subclass/generalization

relation• No built-in modeling constructs in OWL• Different types of part-whole relations exist

– With important semantic differences

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UML Aggregation• Aggregation denotes a binary association

in which one side is an "assembly" and the other side a "part".

• "Assembly" and "part" act as predefined roles involved in the aggregation association.

• Cardinality of a part can be defined – precisely one; optional (0-1); many, ...

• No semantics in UML!

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Aggregation example in UML

audiosystem

tape deck

CD player

tuner

amplifier

speakerheadphones

recordplayer

0-1

0-1

0-1

0-1 0-1 2,4

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UML Composition• Sub-type of aggregation• Existence of part depends on aggregate

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Aggregation vs. generalization• Similarities:

– Tree-like structure– Transitive properties

• Differences:– AND-tree (aggregation) vs. OR-tree

(generalization)– instance tree (aggregation) vs. class tree

(generalization)

Examples: partOf or subClassOf?

• House – Building• Brick – House• Antique book – Antique book collection• Silvio – Married Couple• Hand – Body part• Finger ‐ Hand

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Confusion with non-compositional relations• Temporal topological inclusion

– The customer is in the store, but not part of it• Classification inclusion

– A Bond movie is an instance of “film” but part of my film collection

• Attribution– The height and width of a ship are not part of the ship

• Attachment– A wrist watch is not part of the wrist

• Ownership– I own a bicycle but it is not part of me

Types of part‐whole relations

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Types of part-whole relationsBased on three distinctions

1. Configurability Functional/structural relation with the other parts

or the whole yes/no

2. Homeomerous Parts are same kind as the whole yes/no

3. Invariance Parts can be separated from the whole

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Component-integral• Functional/structural relation to the whole• Parts can be removed and are different

from whole• Organization of the parts• Examples: car wheels, film scenes• N.B. difference between “wheel” and “car

wheel”

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Material-object• Invariant configuration• Examples:

– A bicycle is partly iron– Wine is partly alcohol– Human body is partly water

• The “made-off” relation• Relation between part and whole is not

known

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Portion-object• Homeomeric configuration of parts• Examples:

– A lice of bread is part of a loaf of bread– A sip of coffee is part of a cup o coffee

• Portions can be quantified with standard measures (liter, gram, ..)

• Homeomeric: a sip of coffee is coffee (but a bicycle wheel is not a bicycle)– Ingredients of portion and object are the same

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Place-area• Homeomeric invariant configuration• Examples:

– North-Holland is part of The Netherlands– The Mont Blanc peak is part of the Mont Blanc

mountain– The head is part of the human body (?!)

• Typically between places and locations

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Member-bunch• No configuration, no invariance, not

homeomeric• Members of a collection• Examples:

– A tree is part of a wood– The hockey player is part of a club

• Differentiate from classification-based collections– A tree is a member of the class of trees

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Member-partnership• Same as member-bunch, but invariant• If a part is removed, the whole ceases to

exist• Examples:

– Bonny and Clyde– Laurel and Hardy– A married couple

Example: types of part of relations

• Vitamin – Orange• Branch – Tree• Student – the class of ’02• Book – library• Chair – Faculty Board• Engine – Car• Artuicle - newspaper

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Transitivity of part-whole types

• Transitivity does not (necessarily) hold when traversing different types of part-whole relation– I am a member of a club (member-bunch)– My head is part of me (place-area)– But: my head is not a part of the club