Title: Ontologies and Classifications
1Ontologies and Classifications
- Nicola Guarino
- Laboratory for Applied Ontology (LOA)
- Institute for Cognitive Sciences and Technologies
(ISTC-CNR) - Trento, Italy
www.loa-cnr.it
2Summary
- 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
4Functions 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.
5A simple classification
Whats the meaning of these terms? Whats the
meaning of arcs? they do not represent analytic
relationships!
6The source of all problems different languages,
different conceptualizations
7A 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
8Standard 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
9The 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
10What is an ontology
11Ontology, 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.
12Ontology 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
13What 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.
14An example the concept of red
a b
a
b
a,b
15What 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
16Language L
Good
17Ontology Quality Precision and Coverage
High precision, max coverage
Low precision, max coverage
Max precision, limited coverage
Low precision, limited coverage
18Why precision is important
Possible interpretations of apple
Area of falseagreement!
19Ontologies and...
20Levels 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
21Ontologies and taxonomies
22Ontologies 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
23Ontologies 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
24A 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
25Which 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
26The semantic web architecture Tim Berners Lee
2000
27Formal 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
28When 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.
29Role 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.
30Conclusions
- 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
31A 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