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lecture 2: ontology - basics

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ontology

a branch of metaphysics relating to the natureand relations of being

a particular theory about the nature of being or the kinds of existence

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ontology & historytree of Porphyry

Supreme: SUBSTANCEDifferentiae: material immaterialSubordinate: BODY SPIRITDifferentiae: animate inanimateSubordinate: LIVING MINERALDifferentiae: sensitive insensitiveSubordinate: ANIMAL PLANTDifferentiae: rational irrationalSubordinate: HUMAN BEAST

Individuals: Socrates Plato Aristotle etc.

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ontologygeneric

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ontologydomain-based

the subject of ontology is the study of the categories of things that exist or may exist in some domain

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ontologydomain-based

the product of such a study, called an ontology, is a catalog of the types of things that are assumed to exist in a domain of interest from the perspective of a person who uses a specific language for the purpose of talking about the domain

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ontologydomain-based – definition 1

a formal, explicit specification of a shared conceptualization

[T.Gruber, 1993]

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ontologydomain-based

conceptualization refers to an abstract model of phenomena in the world by having identified the relevant concepts of those phenomena

explicit means that the type of concepts used, and the constraints on their use are explicitly defined

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ontologydomain-based

formal refers to the fact that the ontology should be machine readable

shared reflects that ontology should capture consensual knowledge accepted by the communities

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ontologydomain-based – definition 2 (W3C)

ontology is a term borrowed from philosophy that refers to the science of describing the kinds of entities in the world and know they are related

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ontology… description of …

classes (“things”) in the various domains of interest

relationships among those “things” properties (attributes) that “things” should

possess

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ontologyexample

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ontologyexample

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ontologyvs taxonomy

taxonomy the study of the general principles of scientific classification – systematicsclassification – especially – orderly classification of plans and animals according to their presumed natural relationships

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ontologyvs taxonomy

taxonomy classifies terms hierarchically, using (generalization, is-a, or type-of) relationship- no other relationships- no attributes/features describing terms

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ontologyvs taxonomy (example)

- Linnaean living being taxonomyKingdom: animalia Filo: chordata

Subfilo: vertebrata Class: mamalia

Subclass: theria Order: primata

Suborder: anthropoidea Family: hominidae Genera: homo

Species: sapiens

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ontologyvs taxonomy (example)

- directory structure in a personal computer

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ontologyvs thesauri

thesauri contains a set of relationships among concepts, organized in a taxonomic way

it is a taxonomy with a set of semantic (binary) relationships, such as, equivalence, inverse, and association

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ontologyvs thesauri

not sufficient to model other (part-of, member-group, cause-effect, …) aspects of real world

the most popular thesaurus - WordNet

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ontologyvs thesauri - WordNet

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ontologyvs thesauri - WordNet

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ontologyvs thesauri - WordNet

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ontology”unique” properties – 1

strict subconcept hierarchy organization of terms must follow the generalization relationship – is-a, type-of relationship

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ontology”unique” properties – 2

ambiguity-free interpretation of meanings and relationshipsusers may define properties (with values restricted to certain domains) and more expressive relationships (part-of, ……………)

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ontology”unique” properties – 3

the use of a controlled, finite, but extensible vocabulary

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ontologyclassification according to semantic spectrum

based on the internal structure and contents of ontolgoies

depends on the complexity and sophistication of the elements

the spectrum ranges from informal catalogues of terms to sophisticated ontologies

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ontologyclassification according to semantic spectrum

- controlled vocabularies (finite lists of terms)- glossaries (lists of terms whose meaning is

described in natural language)- Thesauri (lists of terms … and specific

relationships between the terms)

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ontologyclassification according to semantic spectrum

- informal is-a hierarchies (hierarchies that use generalization relationships in an informal way – not rigorously)

- formal is-a hierarchies (hierarchies that fully respect the generalization relationships)

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ontologyclassification according to semantic spectrum

- frames (models that include classes and properties; the primitives of the frame model are classes, or frames, that have properties called slots or attributes; slots may contain default values, refer to other frames, or contain different methods)

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ontologyclassification according to semantic spectrum

- ontologies that express value restrictions (contain constructs for restricting the values the class properties can assume)

- ontologies that express logical restrictions (allow first-order logic restrictions to be expressed)

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ontologyclassification according to ontology generality

- upper-level ontologies (describe generic concepts, such as space, time, events …)

- domain ontologies (describe vocabulary pertaining to a given domain, by specializing the concepts provided by the upper-level ontology)

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ontologyclassification according to ontology generality

- task ontologies (describe vocabulary required to perform generic tasks or activities, by specializing the concepts provided by the upper-level ontology)

- applications ontologies (describe vocabulary of a specific application, whose concepts correspond to the roles performed by entities in a given domain while performing some task or activity)

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ontologyclassification according to represented info

based on “orthogonal”, to previous slides, classification

- knowledge-representation ontologies (provide primitive modeling elements – classes, subclasses, value, …)

- generic and common use ontologies (represent common-sense knowledge that can be used in different domains; vocabulary that relates classes, events, space, causality, and behavior)

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ontologyclassification according to represented info

- upper ontologies (describe general concepts, for example SUMO)

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ontologyclassification according to represented info

- domain ontologies (offer concepts that can be reused in a specific domain – medical, law, …; sth between upper and domain ontologies)

- task ontologies (describe vocabulary related to a task or activity)

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ontologyclassification according to represented info

- domain-task ontologies (are task ontologies that can be reused in one specific domain)

- method ontologies (provide definitions for concepts and relationships relevant to a process)

- application ontologies (contain all necessary concepts to model the application in question)

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ontologydescription languages

1967 – markup language (structure of documents with help of tags)

SGML – Standard Generalization Markup Language

1989 – HTML (HyperText Markup Language)XML (Extensible Markup Language)

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ontologydescription languages

RDF (Resource Markup Language) – representing information about resources in the web

RDF SchemaSHOE (Simple HTML Ontology Extension)Oil (Ontology Inference Layer)DAML (DARPA Agent Markup Language)

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ontologydescription languages

2001 – DMAL+OilFeb 10th, 2004 – OWL (Web Ontology

Language)

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