Date post: | 05-Dec-2014 |
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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