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Ontologies and Classifications

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Title: Ontologies and Classifications


1
Ontologies and Classifications
  • Nicola Guarino
  • Laboratory for Applied Ontology (LOA)
  • Institute for Cognitive Sciences and Technologies
    (ISTC-CNR)
  • Trento, Italy

www.loa-cnr.it
2
Summary
  • Classifications have a central role within
    information architecture
  • Proper use of classifications requires
    understanding their terms
  • Especially in presence of multiple, heterogeneous
    classifications
  • Main role of computational ontologies is to
    clarify the meaning of terms
  • Therefore, ontology is not just a trendy name
    for classification

Ontologies and classifications play complementary
roles in information architecture
3
  • Functions of classifications in information
    architecture
  • The problem understanding, sharing, integrating
    meaning
  • What are ontologies
  • Foundational vs. lightweight ontologies
  • The role of foundational ontologies
  • Ontologies as complementary to classifications

4
Functions of classifications
  • Support information retrieval and analysis.
  • partition the search space on the base of
    pre-determined criteria (encoded by syntactic
    keys)
  • Provide triggers for action.

5
A simple classification
Whats the meaning of these terms? Whats the
meaning of arcs? they do not represent analytic
relationships!
6
The source of all problems different languages,
different conceptualizations
7
A first solution glossaries and thesauri
  • Glossaries link terms to concepts, described
    informally by glosses
  • Thesauri add structural relationships
    (generalization, part, dependence, causation)
    among terms (and concepts).
  • Multilingual glossaries and thesauri are
    available for many domains.
  • General thesauri (e.g., WordNet) are available
    for many languages

8
Standard glossaries and thesauri can help, but...
  • Defining standard vocabularies is difficult and
    time-consuming
  • Once defined, standards dont adapt well
  • Heterogeneous domains need a broad-coverage
    vocabulary
  • People dont implement standards correctly anyway
  • Vocabulary definitions are often ambiguous or
    circular
  • Accessing and integrating heterogeneous
    glossaries and thesauri becomes a nightmare

9
The need to focus on CONTENT
  • The key problems
  • content-based information access (semantic
    matching)
  • content-based information integration (semantic
    integration)
  • To approach them, content must be studied,
    understood, analyzed as such, independently of
    the way it is represented.
  • Computer technologies are not really good for
    that (focus is usually on representation and
    reasoning)
  • A strong interdisciplinary approach is needed

10
What is an ontology
11
Ontology, lexicon, semantics
  • Distinctions among contents Ontology (capital
    o)
  • Reference to content Lexicon, via Semantics
  • Every organization, every computer system
  • Makes (implicit) ontologic assumptions
  • Adopt a certain lexicon, to which an intended
    semantics is ascribed.

12
Ontology and Ontologies
  • Ontology the philosophical discipline
  • Study of the nature and structure of being qua
    being
  • (content qua content)
  • ontologies

Specific (theoretical or computational)
artifactsexpressing the intended meaning of a
vocabularyin terms of primitive categories and
relations describingthe nature and structure of
a domain of discourse
Gruber Explicit and formal specifications of a
conceptualization
13
What is a conceptualization
  • The implicit rules used to structure reality as
    perceived and organized by an agent,
    independently of
  • the vocabulary used
  • the actual occurence of a specific situation
  • Different situations involving same objects,
    described by different vocabularies, may share
    the same conceptualization.

14
An example the concept of red
a b
a
b
a,b

15
What is a conceptualization?A cognitive approach
  • Humans isolate relevant invariances from
    physical reality (quality distributions) on the
    basis of
  • Perception (as resulting from evolution)
  • Cognition and cultural experience (driven by
    actual needs)
  • (Language)
  • A set of atomic stimuli (input pattern) is
    received when the attention is focused on a
    phenomenon in a certain minimal region of
    spacetime (a single presentation)
  • Synchronic level topological/morphological
    invariants within a single presentation
  • Unity properties are ascribed to input patterns
    topological and morphological wholes (percepts)
    emerge
  • Diachronic level temporal invariants across
    multiple presentations
  • Objects equivalence relationships among percepts
    belonging to different presentations
  • Events unity properties are ascribed to percept
    sequences belonging to different presentations

16
Language L
Good
17
Ontology Quality Precision and Coverage
High precision, max coverage
Low precision, max coverage
Max precision, limited coverage
Low precision, limited coverage
18
Why precision is important
Possible interpretations of apple
Area of falseagreement!
19
Ontologies and...
20
Levels of Ontological Precision
game(x) ? activity(x) athletic game(x) ?
game(x) court game(x) ? athletic game(x) ? ?y.
played_in(x,y) ? court(y) tennis(x) ? court
game(x) double fault(x) ? fault(x) ? ?y.
part_of(x,y) ? tennis(y)
game athletic game court game tennis
outdoor game field game football
tennis football game field game court
game athletic game outdoor game
Axiomatic theory
Taxonomy
game NT athletic game NT court game RT
court NT tennis RT double fault
Glossary
DB/OO scheme
Catalog
Thesaurus
Ontological precision

21
Ontologies and taxonomies
22
Ontologies vs. classifications
  • Classifications focus on
  • access, based on pre-determined criteria
    (encoded by syntactic keys)
  • Ontologies focus on
  • Meaning of terms
  • Nature and structure of a domain

23
Ontologies vs. Database Schemas
  • Database schemas
  • Constraints focus on data integrity
  • Relationships and attribute values out of the DoD
  • Typically non-executable
  • Ontologies
  • Constraints focus on intended meaning
  • Relationships and attribute values first class
    citizens
  • Typically executable

24
A single, imperialistic ontology?
  • An ontology is first of all for understanding
    each other
  • ...among people, first of all!
  • not necessarily for thinking in the same way
  • A single ontology for multiple applications is
    not necessary
  • Different applications using different ontologies
    can co-exist and co-operate (not necessarily
    inter-operate)
  • ...if linked (and compared) together by means of
    a general enough basic categories and relations
    (primitives).
  • If basic assumptions are not made explicit, any
    imposed, common ontology risks to be
  • seriously mis-used or misunderstood
  • opaque with respect to other ontologies

25
Which primitives? The role of ontological
analysis
  • Theory of Essence and Identity
  • Theory of Parts (Mereology)
  • Theory of Wholes
  • Theory of Dependence
  • Theory of Composition and Constitution
  • Theory of Properties and Qualities

The basis for a common ontology vocabulary
26
The semantic web architecture Tim Berners Lee
2000
27
Formal Ontology
  • Theory of formal distinctions and connections
    within
  • entities of the world, as we perceive it
    (particulars)
  • categories we use to talk about such entities
    (universals)
  • Why formal?
  • Two meanings rigorous and general
  • Formal logic connections between truths -
    neutral wrt truth
  • Formal ontology connections between things -
    neutral wrt reality

28
When is a precise (and well-founded) ontology
useful?
  • When subtle distinctions are important
  • When recognizing disagreement is important
  • When careful explanation and justification of
    ontological commitment is important
  • When mutual understanding is more important than
    interoperability.

29
Role of ontologies in information
architecture (thanks to Dagobert Soergel)
  • Relate concepts to terms. Clarify their meaning
    by providing a system of definitions.
  • Provide a semantic road map and common conceptual
    reference tool across different disciplines,
    languages, and cultures
  • Make medical concepts clear to social science
    researchers and vice versa
  • Improve communication. Support learning by
    helping the learner ask the right questions
  • Support information retrieval and analysis
  • Support the compilation and use of statistics
  • Support meaningful, well-structured display of
    information.
  • Support multilinguality and automated language
    processing
  • Support reasoning.

30
Conclusions
  • In general, classifications are not ontologies
  • Some classifications are ontologies
  • Ontologies are needed to understand, integrate,
    reason on classifications
  • Every ontology induces a classification
  • Both ontologies and classifications are a
    fundamental tool for information architecture

31
A new journal Applied Ontology
Editors in chief Nicola Guarino ISTC-CNR Mark
Musen Stanford University IOS Press Amsterdam,
Berlin, Washington, Tokyo, Beijing www.applied-ont
ology-org
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