Introductory lecture on ontologies for VU Knowledge & Media course

1. Ontologies:
vehicles for reuse
Course “Knowledge & Media”
September 2015
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2. Overview
• The notion of ontology
• Common ontologies
• Example ontology engineering topic:
– Part-whole relations
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3. The notion of ontology
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4. Concepts
• Help us organize the world around us
• Act as recognition device
• Test for reality
• We use many different types of concepts

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

6. The concept triad
Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

7. 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”

8. Incomplete concept specifications
• Are common
• Think of an example:
– Concept with no instances
– Concept with no symbol
• Primitive vs. defined concepts

9. 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.

10. What is an Ontology?
“explicit specification of a shared
conceptualization that holds in a particular
context”
(Gruber’s definition in extended form)

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

12. 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)

13. Context and Domain
Principle 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.”

14. 14
Top-level categories:
many different proposals
Chandrasekaran et al. (1999)

15. 15
The is-a hierarchy

16. Classes as instances
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Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

17. 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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18. 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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19. Basic-level categories
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20. 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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21. 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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22. COMMON ONTOLOGIES

23. 23
Friend of a Friend (FOAF)
• Describing people:
– names
– depictions
– friends, acquaintances, relations
– organizations
– e-mail addresses
– webpages
– ...
• see http://xmlns.com/foaf/spec/

24. 24
Agents: People and Groups

25. 25
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

26. 26
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/

27. 27
Dublin Core 1.0 Elements
–Title
–Creator
–Subject
–Description
–Publisher
–Contributor
–Date
–Type
–Format
–Identifier
–Source
–Language
–Relation
–Coverage
–Rights

28. 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
• See
http://www.w3.org/TR/owl-time/
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29. Allen’s time relations
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30. PART-WHOLE RELATIONS

31. 31
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

32. 32
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!

33. 33
Aggregation example in UML
audio
system
tape deck
CD player
tuner
amplifier
speakerhead
phones
record
player
0-1
0-1
0-1
0-1 0-1 2,4

34. 34
UML Composition
• Sub-type of aggregation
• Existence of part depends on aggregate

35. 35
Aggregation vs. generalization
• Similarities:
– Tree-like structure
– Transitive properties
• Differences:
– AND-tree (aggregation) vs. OR-tree
(generalization)
– instance tree (aggregation) vs. class tree
(generalization)

36. 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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37. 37
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

38. Types of part whole‐
relations
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39. 39
Types of part-whole relations
Based on three distinctions
1. Configurability
 Functional/structural relation with the other parts
or the whole yes/no
1. Homeomerous
 Parts are same kind as the whole yes/no
1. Invariance
 Parts can be separated from the whole

40. 40
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”

41. 41
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

42. 42
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

43. 43
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

44. 44
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

45. 45
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

46. 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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47. 47
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