1. Ontology evaluation
Course “Ontology Engineering”

2. 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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3. 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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4. Example of applying rigidity
Class Human
hasBodyWeight (rigid)
isFather (anti-rigid)
isFemale (semi-rigid)
hasGender (rigid)
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5. 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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6. Example of identity criteria:
Class Human
• Different bodies
Class Article
• Citation information
Class GeographicalLocation
- Latitude/longitude(/Altitude) coordinates
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7. 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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8. 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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9. 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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10. 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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11. 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 ⊆ Animal
What is the relation between Species and
Human?
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12. Species
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13. Modelling issue:
classes as instances
Aircraft-type Aircraft
no-of-engines: integer >0 no-of-seats: positive integer
propulsion: {propeller, jet} owner: Airline
Fokker-70 Fokker-70
instance of Aircraft-type subclass of Aircraft
no-of-engines = 2 no-of-seats: 60-80
propulsion = jet
PH-851
instance of Fokker-70
no-of-seats = 65
owner = KLM
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14. 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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15. 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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16. 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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17. Example “dirty” hierarchy
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18. Principles for backbone
identification (Rector)
1. Backbone should be a genuine tree
2. 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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19. Example backbone analysis
Hormone Substance
Steroid hormone Enzyme
Cortisol Protein
Protein Hormone Steroid
Insulin Catalyst
ATPase
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20. Backbone:
physical/chemical structure
Substance
Protein
Insulin
ATPase
Steroid
Cortisol
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21. Roles: non-primitive types
PhysiologicalRole
HormoneRole
CatalystRole
Hormone = Substance AND
playsRole HormoneRole
Enzyme = Protein AND
playsRole CatalystRole
Insulin => playsRole HormoneRole
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22. 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
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