Ontology evaluation

Course “Ontology Engineering”

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OntoClean

• Guarino & Welty

• Method for rationalizing subclass hierarchies

• Meta-properties for characterizing classes:– Rigidity– Identity– Unity

• Are used to analyze an existing subsumption hierarchy

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Rigid class properties

• Are “essential” for all its instances– It must always hold, and not just accidentally

• Semi-rigid; essential for some of the instances

• Anti-rigid: not essential for all instances

• Classes intentionally defined on anti-rigid properties cannot be superclasses of classes defined on rigid properties

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Example of applying rigidity

Class Human

hasBodyWeight (rigid)

isFather (anti-rigid)

isFemale (semi-rigid)

hasGender (rigid)

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Identity

• Refers to the problem of being able to recognize objects of a certain class

• Identity criteria:– How do we recognize an object as belonging

to a class?– Should hold over time– How can one determine two instances are the

same or different?– Identity criteria are inherited over the

subsumption relation

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Example of identity criteria:

Class Human• Different bodies

Class Article• Citation information

Class GeographicalLocation- Latitude/longitude(/Altitude) coordinates

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Example of use of Identity

• Does the class TimeDuration (e.g. “1 hour”) subsume the class TimeInterval (e.g. 11:00-12:00 today)?

• Check identity: multiple instances of TimeInterval can be identified as the same instance of TimeDuration

• Compare this to the subsumption relation between Human and Female

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Unity

• How to determine something is a whole?• How to determine which are the parts?• Unit criteria:

– Criteria for essential parts– Criteria for conditions between the parts

• Guideline for analyzing subsumption hierarchies:– Wholes should not be subclasses of non-

wholes

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Examples of unity

• Is “water” a unity?– Not if it has no clear boundaries

• But the following are unities:– An ocean– A cup of water

• Applying the guideline:– Can “water” be a superclass of “ocean”?

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Ontological analysis of a subsumption hierarchy

• Identifying the “backbone”– Subclasses based on rigid properties– Can also help in comparing two hierarchies

• Discovering inconsistencies in hierarchies– List of common types of misuse of

subsumption

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Misuse of subsumption:instantiation• Some cases are easy:

– Asia in not a subclass of Continent, but an instance

– BillClinton is not a subclass of Human, but an instance of it.

• Consider the subclass hierarchy Human Mammal AnimalWhat is the relation between Species and

Human?

Species

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Modelling issue:classes as instances

Aircraft-type

no-of-engines: integer >0

propulsion: {propeller, jet}

Fokker-70

instance of Aircraft-type

no-of-engines = 2

propulsion = jet

Aircraft

no-of-seats: positive integer

owner: Airline

Fokker-70

subclass of Aircraft

no-of-seats: 60-80

PH-851

instance of Fokker-70

no-of-seats = 65

owner = KLM

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Misuse of subsumption:part-whole

• Common error

• E.g. Engine is not a subclass of Car

• See part-of relations lecture

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Type restriction

• Is CarPart a superclass of Engine?– No, there are engines which are not car parts– Engine has rigid properties– Car parts have no rigid properties

=> CarPart cannot subsume Engine

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Polysemy

• Example confusion– This book is heavy– I liked this book

• Using a term in two different senses

• Cf. concept/term debate in thesauri

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Example “dirty” hierarchy

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Principles for backbone identification (Rector)1. Backbone should be a genuine tree2. Distinctions at one level of the subclass

hierarchy should have he same decomposition principle (“dimension”)

e.g. location

3. Self-standing concepts• Disjoint but open: no exhaustive enumeration

possible

4. Partitioning/refining concepts• Properties that carve up the subsumption space in

exhaustive disjoint partitions

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Example backbone analysis

Hormone

Steroid hormone

Cortisol

Protein Hormone

Insulin

ATPase

Substance

Enzyme

Protein

Steroid

Catalyst

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Backbone: physical/chemical structure

Substance

Protein

Insulin

ATPase

Steroid

Cortisol

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Roles: non-primitive types

PhysiologicalRole HormoneRole CatalystRole

Hormone = Substance AND playsRole HormoneRoleEnzyme = Protein AND playsRole CatalystRoleInsulin => playsRole HormoneRole

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Summary

• Construction of subclass hierarchies is error prone

• Techniques for normalization through ontological analysis exist

• Main advantage of normalized hierarchy is ease of understanding by others– Prevention of misunderstandings when

hierarchy is shared