Ontology Engineering: Ontology evaluation


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Ontology Engineering: Ontology evaluation

  1. 1. Ontology evaluationCourse “Ontology Engineering”
  2. 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 2
  3. 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 3
  4. 4. Example of applying rigidityClass Human hasBodyWeight (rigid) isFather (anti-rigid) isFemale (semi-rigid) hasGender (rigid) 4
  5. 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 5
  6. 6. Example of identity criteria:Class Human• Different bodiesClass Article• Citation informationClass GeographicalLocation- Latitude/longitude(/Altitude) coordinates 6
  7. 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 7
  8. 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 8
  9. 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”? 9
  10. 10. Ontological analysis of asubsumption 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 10
  11. 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? 11
  12. 12. Species 12
  13. 13. Modelling issue: classes as instancesAircraft-type Aircraft no-of-engines: integer >0 no-of-seats: positive integer propulsion: {propeller, jet} owner: AirlineFokker-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 13
  14. 14. Misuse of subsumption:part-whole• Common error• E.g. Engine is not a subclass of Car• See part-of relations lecture 14
  15. 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 15
  16. 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 16
  17. 17. Example “dirty” hierarchy 17
  18. 18. Principles for backboneidentification (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. location3. Self-standing concepts • Disjoint but open: no exhaustive enumeration possible4. Partitioning/refining concepts • Properties that carve up the subsumption space in exhaustive disjoint partitions 18
  19. 19. Example backbone analysisHormone SubstanceSteroid hormone EnzymeCortisol ProteinProtein Hormone SteroidInsulin CatalystATPase 19
  20. 20. Backbone:physical/chemical structure Substance Protein Insulin ATPase Steroid Cortisol 20
  21. 21. Roles: non-primitive typesPhysiologicalRole HormoneRole CatalystRoleHormone = Substance AND playsRole HormoneRoleEnzyme = Protein AND playsRole CatalystRoleInsulin => playsRole HormoneRole 21
  22. 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 22