Ontologies and Classifications

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Ontologies and Classifications

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

www.loa-cnr.it
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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
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• 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

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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.

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A simple classification
Whats the meaning of these terms? Whats the
meaning of arcs? they do not represent analytic
relationships!
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The source of all problems different languages,
different conceptualizations
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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

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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

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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

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What is an ontology
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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.

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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
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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.

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

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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

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Language L
Good
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Ontology Quality Precision and Coverage
High precision, max coverage
Low precision, max coverage
Max precision, limited coverage
Low precision, limited coverage
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Why precision is important
Possible interpretations of apple
Area of falseagreement!
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Ontologies and...
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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

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Ontologies and taxonomies
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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

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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

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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

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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
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The semantic web architecture Tim Berners Lee
2000
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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

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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.

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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.

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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

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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