Ontologies What, why and how

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Ontologies - What, why and how?

• Cartic Ramakrishnan
• LSDIS lab
• University of Georgia

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What is Ontology

• The study of being qua being the study of
  possible
• The study of the nature of possible ontology as
  the theory of distinctions among possibilia
• The study of the most general characteristics
  that anything must have in order to count as a
  (certain kind of) being or entity.

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Definitions

• Ontology (capital o)
• a philosophical discipline.
• An ontology (lowercase o)
• specific artifact designed with the purpose of
  expressing the intended meaning of a vocabulary

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What is an ontology?

• A shared vocabulary
• Plus A specification (actually, a
  characterization) of the intended meaning of that
  vocabulary
• ...i.e., an ontology accounts for the commitment
  of a language to a certain conceptualization
• An ontology is a specification of a
  conceptualization Gruber 95

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Models and Conceptualizations
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Capturing Intended Meaning

• First order logic is ontologically neutral
• Logical KBs often rely on natural language to
  convey intended meaning

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Intended Models
An ontology consisting of just a vocabulary is
of little use - Unintended interpretations need
to be excluded
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What is a conceptualization?
Conceptualization of scene 1 lta, b, c, d, e ,
on, above, clear, table gt
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What is a conceptualization?
The same conceptualization?
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What is a conceptualization

• Conceptualization the formal structure of
  reality as perceived and organized by an agent,
  independently of
• the vocabulary used (i.e., the language used)
• the actual occurence of a specific situation
• Different situations involving the same objects,
  described by different vocabularies, may share
  the same conceptualization.

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Relations vs. Conceptual Relations
(Montague-style semantics)
ordinary relations are defined on a domain
D conceptual relations are defined on a domain
space ltD, Wgt
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Ontologies constrain the intended meaning
Conceptualization C
Commitment KltC,Igt
Language L
Models M(L)
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Levels of Ontological Depth(SSK would disagree)

• Lexicon
• Vocabulary with NL definitions
• Simple Taxonomy
• Thesaurus
• Taxonomy plus related-terms
• Relational Model (NOT DB)
• Unconstrained use of arbitrary relations
• Fully Axiomatized Theory

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ontologies - ontology

• Ontology
• study of being as a branch of philosophy
• Ontologies
• result of the analysis of a particular domain of
  interest (possibly as broad as the universe)
• instantiation of a concrete ontological model of
  that domain

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Ontologies-ontology

• Ontologies are to a large extent in principle
  language independent
• Varying scope and content of domain ontologies
• upper-level ontologies (Cyc)
• application ontologies (??)
• task ontologies (??)

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Definitions - Yes, Again!!

• Here are three definitions of domain ontologies
• (i) "System of categories accounting for a
  particular vision of the world." Guarino
• (ii) "Specification of a conceptualization."
  Gruber
• (iii) "Concise and unambiguous description of
  principle relevant entities with their potential,
  valid relations to each other." guess who?

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What an Ontology is NOT!!!

• not a collection of facts arising from a specific
  situation
• not a model of an application domain
• not a database schema
• not a knowledge base
• not a taxonomy
• not a vocabulary or dictionary
• not a semantic net

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Why ontologies?

• Data integration
• Semantic integration of n databases
• without the great o would require nn
  integration attempts
• with the great o would require n attempts
• Data annotation
• full-fledged ontology not required
• since main purpose is fixed unique reference
  point in the for of controlled vocabulary

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ENTER GO!!!

• Not ontology but vocabulary
• ISA vs. instance-of
• PART-OF vs made of, belongsto
• 80 concepts lack explicit defn.
• 700 concepts are orphans
• no clear design principle
• no IC for consistency
• where do new concepts go?
• No grammar rules for to combine concept
• Not The Gene Ontology but 3

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References

• Guarino, N. (1998). Some Ontological Principles
  for Designing Upper Level Lexical Resources. In
  Proceedings of First International Conference on
  Language Resources and Evaluation. Granada,
  Spain.
• Gruber, T. R. (1993). Knowledge Acquisition 5,
  199-220.
• Schulze-Kremer, S. (1998) Ontologies for
  molecular biology