Semantic Web 1989 Tim BernersLee 1991 1994 10

Semantic Web의 탄생 개요 인터넷의 역사 • 1989 Tim Berners-Lee에 의해 창시 • 1991년 일반에 공개 • 1994년 10월 Tim Berners-Lee의 주도로 MIT와 공동으로 W 3 C 설립 웹의 다음 단계의 발전…? ! "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 6

Semantic Web의 구성 시맨틱 웹의 요소 Resource Description Framework Semantic Web Ontology Technique Agent Program 12

XML, RDF 예제 시맨틱 웹의 요소 <? XML version=“ 1. 0”> <employees> List of persons in company: <person name=“John”> <phone>47782></phone> On leave for 2001. </person> </employee> http: //www. w 3. org created by http: //www. w 3. org XML 표현 예 name phone A directed labeled graph representation 항목이 3개 있는 RDF description Object Attribute http: //www. w 3. org Created_by #anonymous_resource name #anonymous_resource phone Value #anonymous_resource “John” 47782 인용 Michel Klein, XML, RDF, and Relatives, IEEE Intelligent System, 2001 16

계층적 구조(2) - RDF 시맨틱 웹의 요소 Resource Description Framework ã Is a declarative language and provides a standard way for using XML to represent metadata in the form of statements about properties and relationships of items (a Web address) on the Web. ã A foundation for processing metadata. ã Ý Provides interoperability between applications that exchange machineunderstandable information on the Web. 18

Simple Explanation of Concepts 시맨틱 웹의 요소 <RDF xmlns="http: //www. w 3. org/1999/02/22 -rdf-syntax-ns#" xmlns: dc="http: //purl. org/dc/elements/1. 1/"> <Description about="http: //www. w 3. org/Press/99 Folio. pdf"> <dc: title>The W 3 C Folio 1999</dc: title> <dc: creator>W 3 C Communications Team</dc: creator> <dc: date>1999 -03 -10</dc: date> <dc: subject>Web development, World Wide Web Consortium, Interoperability of the Web </dc: subject> </Description> </RDF> 21

Basic RDF ã Basic RDF Model Ý ã 시맨틱 웹의 요소 Examples Basic RDF Syntax Basic Serialization Syntax Ý Basic Abbreviated Syntax Ý Schemas and Namespaces Ý 22

Basic RDF Model 시맨틱 웹의 요소 Resources ã Properties ã Statements ã 23

Resources 시맨틱 웹의 요소 Can be anything provided that it has a Web address. ã Can be anything that has a URI; the extensibility of URIs allows the introduction of identifiers for any entity imaginable. ã 24

Properties 시맨틱 웹의 요소 A property is a specific aspect, characteristic, attribute, or relation used to describe a resource. ã Each property has a specific meaning, defines its permitted values, the types of resources it can describe, and its relationship with other properties. ã 25

Statements ã RDF Statement Ý ã 시맨틱 웹의 요소 A specific resource (subject) together with a named property (predicate) plus the value (object) of that property. The object of a statement (the property value) Can be another resource specified by a URI Ý Can be a simple string Ý 26

RDF Model 시맨틱 웹의 요소 Renato Iannella, 1998. 9 RDF Description Property Type Value URI Resource 27

RDF Model… 시맨틱 웹의 요소 Eric Miller, 1998 RDF Description Resource 1 Property Type 3 Property Type 1 Resource 2 Property Atomic Type 4 Value Property Type 2 Resource 3 Atomic Value 28

RDF Example 1 ã 시맨틱 웹의 요소 Ora Lassila is the creator of the resource http: //www. w 3. org/Home/Lassila. 주어 (Subject/Resource) http: //www. w 3. org/Home/Lassila 술어 (Predicate/Property) Creator 목적어 (Object/literal) “Ora Lassila” http: //www. w 3. org/Home/Lassila Creator “Ora Lassila” Simple node and arc diagram 29

RDF Example 2 ã 시맨틱 웹의 요소 http: //www. w 3. org/Home/Lassila has creator something and something has name Ora Lassila and email lassila@w 3. org http: //www. w 3. org/Home/Lassila Property with structured value Creator Name Ora Lassila Email lassila @w 3. org 30

RDF Example 3 • 시맨틱 웹의 요소 The individual reffered to by employee id 85740 is named Ora Lassila and has the email address lassila@w 3. org. The resource http: //www. w 3. org/Home/Lassila was created by this individual. http: //www. w 3. org/Home/Lassila Structured value with identifier Creator http: //www. w 3. org/sttaffid/85740 Name Ora Lassila Email lassila @w 3. org 31

Basic RDF Serialization Syntax 시맨틱 웹의 요소 ã ã ã ã [1] RDF : : = ['<rdf: RDF>'] description* ['</rdf: RDF>'] [2] description : : = '<rdf: Description' id. About. Attr? '>' property. Elt* '</rdf: Description>' [3] id. About. Attr : : = id. Attr | about. Attr [4] about. Attr : : = 'about="' URI-reference '"' [5] id. Attr : : = 'ID="' IDsymbol '"' [6] property. Elt : : = '<' prop. Name '>' value '</' prop. Name '>' | '<' prop. Name resource. Attr '/>' [7] prop. Name : : = Qname [8] value : : = description | string [9] resource. Attr : : = 'resource="' URI-reference '"' [10] Qname : : = [ NSprefix ': ' ] name [11] URI-reference : : = string, interpreted per [URI] [12] IDsymbol : : = (any legal XML name symbol) [13] name : : = (any legal XML name symbol) [14] NSprefix : : = (any legal XML namespace prefix) [15] string : : = (any XML text, with "<", ">", and "&" escaped) 32

Using Default Namespace Syntax 시맨틱 웹의 요소 ã Ora Lassila is the creator of the resource http: //www. w 3. org/Home/Lassila. <? xml version="1. 0"? > <RDF xmlns="http: //www. w 3. org/1999/02/22 -rdf-syntax-ns#" xmlns: s="http: //description. org/schema/"> <Description about="http: //www. w 3. org/Home/Lassila"> <s: Creator>Ora Lassila</s: Creator> </Description> </RDF> 33

Abbreviated Syntax 시맨틱 웹의 요소 <rdf: RDF xmlns: rdf="http: //www. w 3. org/1999/02/22 -rdf-syntax-ns#" xmlns: s="http: //description. org/schema/"> <rdf: Description about=“http: //www. w 3. org/Home/Lassila”> <s: Creator>Ora Lassila</s: Creator> 순서화 문법 </rdf: Description> </rdf: RDF> <rdf: RDF> xmlns: rdf="http: //www. w 3. org/1999/02/22 -rdf-syntax-ns#" xmlns: s="http: //description. org/schema/"> <rdf: Description about=“http: //www. w 3. org/Home/Lassila” 단축형 문법 s: Creator=“Ora Lassila” /> </rdf: RDF> 34

RDF Schema ã 시맨틱 웹의 요소 Provides a framework in which independent communities can develop vocabularies that suit their specific needs and share vocabularies with other communities. 35

Classes and Properties 시맨틱 웹의 요소 <Classes and Resources as Sets and Elements> 37

Classes and Properties 시맨틱 웹의 요소 <Class Hierarchy for the RDF Schema> 38

Ontology의 계층과 다른 계층과의 시맨틱 웹의 요소 관계도 heuristic engine Search Proof Rules Logic Rules Data Ontologies 42

Ontology에 대한 프로젝트 *OIL *** 시맨틱 웹의 요소 DAML+OIL • Product of the **On-to-Knowledge Project • Semantic markup language based on OIL • Standard for the definition and exchange of Ontology • Previous version of the ontology language DAML-ONT. • It allows the definition of classes, relationships, and the possibility of doing inference well. • Similar to OIL • RDF schema extension *OIL: An Ontology Infrastructure for the Semantic Web based ontology language. **On-to-Knowledge: European Project that has goal of developing method and tools that allow to exploit the potential of ontologies in the field of knowledge management. http: //www. ontoknowledge. org ***DAML(DARPA(미국방성고등계획연구국) Agent Markup Language): DARPA program similar in some ways to the On-To-Knowledge project. The main goal of DAML is the developing of language and tools to facilitate the implementation of the Semantic Web. http: //www. daml. org 43

DAML+OIL: an Ontology Language for the Semantic Web

DAML+OIL Design Objectives ã Well designed Intuitive to (human) users Ý Adequate expressive power Ý Support machine understanding/reasoning Ý ã Well defined Clearly specified syntax (obviously) Ý Formal semantics (equally important) Ý ã Extend existing web standards Ý DAML+OIL is built on top of RDF(S) 45

Why Build on RDF ã Provides basic ontological primitives Classes and relations (properties) Ý Class (and property) hierarchy Ý Can exploit existing RDF infrastructure ã Provides mechanism for using ontologies ã RDF triples assert facts about resources Ý Use vocabulary from DAML+OIL ontologies Ý 46

The Cake! DAML+O IL DC XHTML SMIL PICS RDF(S) XML 47

Why RDF Is Not Enough ã Expressive inadequacy Only range/domain constraints (on properties) Ý No properties of properties (unique, transitive, inverse etc. ) Ý No equivalence, disjointness, coverings etc. Ý No necessary and sufficient conditions (for class membership) Ý ã Poorly (un) defined semantics 48

How DAML+OIL Builds ON RDFS ã Extends expressive power Ý Ý Ý Constraints (restrictions) on properties of classes (existential/universal/cardinality) Boolean combinations of classes and restrictions Equivalence, disjointness, coverings Necessary and sufficient conditions Constraints on properties 49

How DAML+OIL Builds ON RDFS ã Provides well defined semantics Meaning of DAML+OIL statements is formally specified Ý Both model theoretic and axiomatic specifications provided Ý Allows for machine understanding and automated reasoning Ý 50

DAML+OIL RDF DAML+OIL ontology is a set of RDF statements ã DAML+OIL defines semantics for certain statements ã Does NOT restrict what can be said ã Ý ã Ontology can include arbitrary RDF But no semantics for non-DAML+OIL statements 51

Well Designed(? ) ã Intuitive to (human) users Ý ã Adequate expressive power Ý ã Supports common ontological idioms Extends RDF in several directions Support for machine understanding/reasoning Designed to be “implementable” Ý No features for which it is difficult or impossible to define clear semantics (e. g. , defaults) Ý Decidable and (empirically) tractable reasoning Ý 52

Why Automated Reasoning? ã Semantic web requires machine understanding (of resource descriptions) Ý ã Reasoning is integral to understanding Supports design and use of ontologies Checking class consistency (e. g. , Skyscraper) Ý Checking/deriving sub. Class. Of hierarchy Ý Particularly useful when ontologies are large, multi -authored and rapidly evolving Ý Also useful when integrating/sharing ontologies Does not tell us how to deal with inconsistencies Ý But we should be able to determine when they exist Ý ã 53