Ontologies and Classifications Nicola Guarino Laboratory for Applied Ontology (LOA) Institute for Cognitive Sciences and Technologies (ISTC-CNR) Trento,
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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
• 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
Pictures
Home Work Vacations
Italy Europe
What’s the meaning of these terms?
What’s the meaning of arcs?
…they do not represent analytic relationships!
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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 don’t adapt well
• Heterogeneous domains need a broad-coverage vocabulary
• People don’t 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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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 vocabulary
in 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.
apple
melasame conceptualization
LI
LE
Ontology
Language L
Intended models for each IK(L)
Ontological commitment K (selects D’D and ’)
Interpretations I
Ontology models
Models MD’(L)
Bad Ontology
~Good
relevant invariants across situations:
D,
Conceptualization
State of affairsState of
affairsPerceivedsituations
Perception Reality
Phenomena
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Ontology Quality: Precision and Coverage
Low precision, max coverage
Less good
Low precision, limited coverage
WORSE
High precision, max coverage
Good
Max precision, limited coverage
BAD
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Possible interpretations of
“apple”
Why precision is important
Area of false
agreement!
What “apple” means for the juice company
What “apple” means for the
farmer
Farmer’s ontology
Company’s ontology
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Levels of Ontological Precision
Ontological precision
Axiomatic theory
Glossary
Thesaurus
Taxonomy
DB/OO scheme
tennisfootballgamefield gamecourt gameathletic gameoutdoor game
game athletic game court game tennis outdoor game field game football
gameNT athletic game NT court game RT court NT tennis RT double fault
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)
Catalog
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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
Idea of Chris Welty, IBM Watson Research Centre, while visiting our lab in 2000
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The semantic web architecture [Tim Berners Lee 2000]
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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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?
1. When subtle distinctions are important
2. When recognizing disagreement is important
3. When careful explanation and justification of ontological commitment
is important
4. 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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