Ontologies and Classifications Nicola Guarino Laboratory for Applied

Ontologies and Classifications Nicola Guarino Laboratory for Applied Ontology (LOA) Institute for Cognitive Sciences and Technologies (ISTC-CNR) Trento, Italy www. loa-cnr. it

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 2

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. 4

A simple classification Pictures Home Work Italy Vacations Europe What’s the meaning of these terms? What’s the meaning of arcs? …they do not represent analytic relationships! 5

The source of all problems: different languages, different conceptualizations

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. , Word. Net) are available for many languages 7

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 8

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 9

What is an ontology

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. 11

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) artifacts expressing the intended meaning of a vocabulary in terms of primitive categories and relations describing the nature and structure of a domain of discourse Gruber: “Explicit and formal specifications of a conceptualization” 12

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. LE apple same conceptualization LI mela 13

An example: the concept of red a b {a} {b} {a, b} {} 14

Conceptualization Perception Reality relevant invariants across situations: D, State of State affairsof Perceived affairs Phenomena situations Ontological commitment K (selects D’ D and ’ ) Language L Interpretations I Intended models for each IK(L) Models MD’(L) Bad Ontology ~Good Ontology models

Ontology Quality: Precision and Coverage Good High precision, max coverage BAD Max precision, limited coverage Less good Low precision, max coverage WORSE Low precision, limited coverage 17

Why precision is important Possible interpretations of “apple” Farmer’s ontology Company’s ontology Area of false agreement! What “apple” means for the farmer What “apple” means for the juice company 18

Ontologies and. . .

Levels of Ontological Precision tennis football game field game court game athletic game outdoor game(x) activity(x) athletic game(x) court game(x) athletic game(x) y. played_in(x, y) court(y) tennis(x) court game(x) double fault(x) y. part_of(x, y) tennis(y) game athletic game court game tennis outdoor game field game football Taxonomy Glossary Catalog game NT athletic game NT court game RT court NT tennis RT double fault Thesaurus Axiomatic theory DB/OO scheme Ontological precision 20

Ontologies and taxonomies analytic relationships among terms! 21

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 22

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

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 cooperate (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 24

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 25

The semantic web architecture [Tim Berners Lee 2000] 26

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 27

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. 28

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. 29

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 30

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-ontology-org