74.419 Artificial Intelligence 2004 Ontology

• Ontology Languages • Semantic Web • "Real" Ontologies

Ontology Languages

LOOM – DL based language by Bob McGregor, ISI, USC, Los Angeles Classic – DL based language by Deborah McGuiness, Alex Borgida et al., ATT Bell Labs Ontolingua – KB development tool (with predefined Ontology), Stanford U. Semantic Web – Ontology languages for Internet organization and search (DAML, OIL, OWL), see W3C

1 Ontologies

Wordnet – based on linguistic descriptions Ontosaurus – Ontology used with LOOM Cyc, OpenCyc – Knowledge Base organization system Ontolingua – KB development tool with predefined Ontologies, Stanford U. Microcosmos – Ontology developed for Computational Linguistics, CRL

Semantic Web - Ontology

General Ontology Languages (similar to LOOM, based on DL) for the WWW

2 Semantic Web Definition: The Semantic Web is the representation of data on the World Wide Web. It is a collaborative effort led by W3C with participation from a large number of researchers and industrial partners. It is based on the Resource Description Framework (RDF), which integrates a variety of applications using XML for syntax and URIs for naming. "The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation." -- Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web, Scientific American, May 2001

OWL, OIL, and DAML

• DAML - DARPA Agent Markup Language • OIL - Ontology Inference Engine • DAML+OIL - "semantic markup language for Web resources" • integrate Ontology Language with the Resource Description Framework (RDF) • OWL - Web Ontology Language (follower of DAML and OIL; based on DL) • Developed by the WWW Consortium: W3C.

3 RDF - Example

"Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila."

Subject (Resource) http://www.w3.org/Home/Lassila

Predicate (Property) Creator

Creator Object (literal) "Ora Lassila"

Figure 1: RDF - structure

Figure 2: RDF - Simple node and arc diagram

RDF - Example

"Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila."

Subject (Resource) http://www.w3.org/Home/Lassila

Predicate (Property) Creator

Creator Object (literal) "Ora Lassila"

Ora Lassila

Figure 2: From RDF to XML

4 RDF - Example The individual referred to by employee id 85740 is named Ora Lassila and has the email address [email protected]. The resource http://www.w3.org/Home/Lassila was created by this individual.

Figure 3: RDF - Structured value with identifier

DAML+OIL

"DAML+OIL is a semantic markup language for Web resources. It builds on earlier W3C standards such as RDF and RDF Schema, and extends these languages with richer modelling primitives. DAML+OIL provides modelling primitives commonly found in frame-based languages. DAML+OIL (March 2001) extends DAML+OIL (December 2000) with values from XML Schema datatypes. [...] The language has a clean and well defined semantics."

5 DAML+OIL - Example

Concept Definition (multiple superclasses): a Man is a Male Person

DAML+OIL - Example

Relation Definition hasParent is a relation between animals

6 OWL - Main Language Constructs

RDF Schema Features: • Class • rdf:Property • rdfs:subClassOf • rdfs:subPropertyOf • rdfs:domain • rdfs:range • Individual

OWL - Equality Expressions

(In)Equality: • equivalentClass • equivalentProperty • sameAs (for Individuals) • differentFrom (for Individuals) • allDifferent (for several Individuals)

7 OWL - Combine Class Expressions

• Boolean Combinations of Class Expressions: • unionOf • intersectionOf • complementOf

OWL - Class Axioms

Class Axioms: • oneOf (describe enumerated classes) • disjointWith • equivalentClass (for class expressions) • rdfs:subClassOf (for class expressions)

8 OWL- Properties

Property Characteristics: • InverseOf • TransitiveProperty • SymmetricProperty • FunctionalProperty • InverseFunctionalProperty

OWL- Properties Property Type Restrictions: • allValuesFrom • someValuesFrom Filler Information: • hasValue Arbitrary Cardinality: • minCardinality • maxCardinality • cardinality

9 Web References - Semantic Web

RDF Home Page http://www.w3.org/RDF/ DAML Home Page http://www.daml.org/ O'Reilley XML.com, Introduction to DAML http://www.xml.com/pub/a/2002/01/30/daml1.html OIL Home Page http://www.ontoknowledge.org/oil/ Web Ontology / OWL Home Page http://www.w3c.org/2001/sw/WebOnt/ W3C Home Page http://www.w3c.org/

Ontology - Contents

How to fill this framework given by general Ontology Languages?

10 What is Ontology? - version1

" (From philosophy) An explicit formal specification of how to represent the objects, concepts and other entities that are assumed to exist in some area of interest and the relationships that hold among them." (Free On- line Dictionary of Computing)

What is Ontology? - version 2

"That department of the science of metaphysics which investigates and explains the nature and essential properties and relations of all beings, as such, or the principles and causes of being." (Webster's) "the metaphysical study of the nature of being and existence" (WordNet) " A systematic account of Existence." (Free On-line Dictionary of Computing) The analysis and description of how the world is structured. (my definition)

11 "Real" Ontology

Ontology • looks for semantic and ontological primitives and concepts to describe aspects or parts of “the world” • aim of research is to develop KBs which can be shared and commonly used in various contexts, i.e. for different applications and different fields (e.g. for NLP, reasoning, planning etc.) • relates to psychology and philosophy, as well as data bases and object-oriented programming systems

Constructing Ontologies

Basic elements of ontology languages • Concepts & IS-A Hierarchy • Roles, Relations w. specification • Features, Attributes, Slots w. specification ------• Instances (concrete objects) • Assertions (facts about objects in the world) ------• Axioms (define the world; describe general rules of the world)

12 Reasoning with Ontologies

• Classifier • Consistency Check • Check for Implied Relatonships • Compare and Combine Different Ontologies

Ontologies – Background

Ontology – Conceptual Hierarchy Wittgenstein (philosophy and language) – “Family Resemblances” instead of exact concept definitions Eleanor Rosch (cognitive psychology) – Prototype Theory; natural concepts

13 Basic Concepts in Ontologies

• Physical Objects ("Things") – Stuff and Things; Composite Objects – Fluids – Substances • Abstract Objects ("Ideas") – abstract concepts (ideas) like 'freedom' – difficult to define and describe – also mathematical concepts – intermediate concepts (model properties)

Basic Concepts in Ontologies

• Actions and Events – have time dimension – agent (actions) or natural cause or no cause (events) – modeling of dynamic aspect problematic • Physical Structures – Time – Space • Mathematical Structures – Numbers – Sets, Groups, ...

14 Basic Concepts in Ontologies

• Physical Properties (visual, haptic,auditory...) – weight – spatial measures – colour – size – volume – shape – texture – temperature – hardiness

Basic Concepts in Ontologies

• Concepts representing Property Values – (qualitative) weight values – colours – (qualitative) size values – (qualitative) volume values – shapes – textures – (qualitative) temperatures – (qualitative) hardiness

15 Basic Concepts in Ontologies

• More Concepts and Properties – emotional states – social attributes – social behaviours (difficult) ® deontic logic

Ontology Languages

16 Ontology Languages and Ontologies

Web References - DL, Ontology

Ontology Home Page www.kr.org.top LOOM www.isi.edu/isd/LOOM/LOOM-HOME.html LOOM Ontosauros (Ontology Browser) http://www.isi.edu/isd/ontosaurus.html Ontolingua Home Page www.ksl.stanford.edu/software/ontolingua/ Open Cyc www.opencyc.org/

17 Web References - DL, Ontology

CLASSIC Home Page http://www.bell-labs.com/project/classic/