Semantic Web and Its Applications Ching-Long Yeh 葉慶隆 Department of Computer Science and Engineering Tatung University Taipei, Taiwan Email: [email protected].

Semantic Web and Its ApplicationsSemantic Web and Its Applications

Ching-Long Yeh 葉慶隆Department of Computer Science and Engineering

Tatung UniversityTaipei, Taiwan

Email: [email protected]://www.cse.ttu.edu.tw/chingyeh

Web Technology EvolutionWeb Technology Evolution

SW & Applications 3

Web TechnologyWeb Technology

• HTML• XML• Electronic Business• Semantic Web

SW & Applications 4

InformationPool

WWWWWW

HTTP (Hyper Text Transport Protocol)HTML (Hyper Text Markup Language)URL (Uniform Resource Locator)

Web server

ApplicationClient

HTTP

URL

HTML Document

• Human-to-machine interaction• Information explosion

SW & Applications 5

InformationPool

Interaction Using XML

XML (eXtensible Markup Language)SOAP (Simple Object Access Protocol)

SOAP server

Application

HTTP

XML Document

• Machine-to-machine interaction • Service automation

SOAP server

Application

InformationPool

XML Document

SW & Applications 6

Web Service Architecture

Serviceregistry

Servicerequester

Serviceprovider

FindWSDL, UDDI

PublishWSDL, UDDI

Bind

Servicedescriptions

Servicedescriptions

Services

SW & Applications 7

Electronic Business

Transport, routing, packaging

Business processes,business documents

Company ACompany B

Transport, routing, packaging

Business processes,business documents

ERPERP

• Application-to-Application• Business Process Automation• RosettaNet• ebXML

SW & Applications 8

Semantic WebSemantic Web

• The Semantic Web is a vision:

• See “W3C Semantic Web Activity,” by Marja-Riitta Koivunen, for more descriptions.

the idea of having data on the web defined and linked in a way that it can be used by machines not just for display purposes, but for automation, integration and reuse of data across various applications

http://www.w3.org/Talks/2001/1102-semweb-fin/Overview.html

SW & Applications 9

Semantic WebSemantic Web

• The Semantic Web is the new generation of the World Wide Web, based on the semantic network knowledge representation formalism, which enables packaging information in the form of object-attribute-value statements, so called triples.

• By assuming that terms used in these statements are based on the formally specified meaning (for the community of interest), i.e. ontologies, these triplets can be semantically processed by machine agents.

From: http://www2002.org/CDROM/poster/130.pdf

SW & Applications 10

The Semantic Web Layered ArchitectureThe Semantic Web Layered Architecture

(http://www.w3.org/2001/Talks/0228-tbl/slide5-0.html)

Tim Berners-Lee:“Axioms, Architecture and Aspirations”W3C all-working group plenary Meeting28 February 2001

URI Unicode

XML Namespaces

XML Schema

Sig

RDF M&S

RDF Schema

Ontology

Rules

Logic

Proof

Trust


A Metadata Layer View of the SWA Metadata Layer View of the SW

Resources on the WWW

Metadata layer upon the WWWSchema in OWLInstances in RDF

Semantic Web LanguagesSemantic Web Languages


What is XML?What is XML?

• Extensible Markup Language• A Syntax for Documents • A Meta-Markup Language• A Structural and Semantic Language, not a Formatting

Language• Not just for Web pages


XML StandardsXML Standards

• DTD• Namespace• Schema• DOM• CSS, XSL-T, XSL-FO• XLink• XPointer


XML Protocol: SOAPXML Protocol: SOAP


RDF M&SRDF M&S• RDF (Resource Description Framework)

– Beyond Machine readable to Machine understandable

• RDF consists of two parts– RDF Model (a set of triples)– RDF Syntax (different XML serialization syntaxes)

• RDF Schema for definition of Vocabularies (simple Ontologies) for RDF (and in RDF)


RDF Data ModelRDF Data Model• Resources

– A resource is a thing you talk about (can reference)– Resources have URI’s– RDF definitions are themselves Resources (linkage, see

requirement 1)

• Properties – slots, define relationships to other resources or atomic values

• Statements– “Resource has Property with Value”– (Values can be resources or atomic XML data)

• Similar to Frame Systems


A Simple ExampleA Simple Example• Statement

– “Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila”

• Structure– Resource (subject) http://www.w3.org/Home/Lassila– Property (predicate) http://www.schema.org/#Creator– Value (object) "Ora Lassila”

• Directed graph

http://www.w3.org/Home/Lassilas:Creator

Ora Lassila


EmailName

s:Creator

http://www.w3.org/Home/Lassila

Another ExampleAnother Example

• To add properties to Creator, point through an intermediate Resource.

Person://fi/654645635

Ora Lassila [email protected]


Example:Example: Bag Bag

• The students incourse 6.001 are Amy, Tim,John, Mary,and Sue

Rdf:Bag

/Students/Amy

/Students/Tim

/Students/John

/Students/Mary

/Students/Sue

bagid1

/courses/6.001

students

rdf:type

rdf:_1

rdf:_2

rdf:_3

rdf:_4

rdf:_5


rdf:_1

rdf:_2

rdf:_3

rdf:typesource

ftp.eu.net

ftp.cs.purdue.edu

ftp.x.org

Example:Example: Alternative Alternative

• The source code for X11 may be found at ftp.x.org, ftp.cs.purdue.edu, or ftp.eu.net

altid

rdf:Althttp://x.org/package/X11


RDF Schema (RDFS)RDF Schema (RDFS)

• RDF just defines the data model

• Need for definition of vocabularies for the data model - an

Ontology Language!

• The RDF Schema mechanism provides a basic type system for

use in RDF models.

• The RDF schema specification language is less expressive, but

much simpler to implement, than full predicate calculus languages

such as CycL and KIF.


Most Important Modeling PrimitivesMost Important Modeling Primitives

• Core Classes– Root-Class rdfs:Resource

– MetaClass rdfs:Class

– Literals rdfs:Literal

• rdfs:subclassOf-property

• Inherited from RDF: properties (slots)

• rdfs:domain & rdfs:range

• rdfs:label, rdfs:comment, etc.

• Inherited from RDF: InstanceOf (rdf:type)


OWLOWLW3C Web Ontology LanguageW3C Web Ontology Language

• OWL provides three increasingly expressive sublanguages: OWL Lite, OWL DL, and OWL Full.


OWLOWLW3C Web Ontology LanguageW3C Web Ontology Language

OWL Lite language constructs

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

(In)Equality: equivalentClass equivalentProperty sameAs differentFrom allDifferent

Property Characteristics: inverseOf TransitiveProperty SymmetricProperty FunctionalProperty InverseFunctionalProperty

Property Type Restrictions: allValuesFrom someValuesFrom

Restricted Cardinality: minCardinality (only 0 or 1) maxCardinality (only 0 or 1) cardinality (only 0 or 1)

Header Information: ontology imports


The Big Picture of SW

(http://semanticweb.org/about.html#bigpicture)


Uses Cases of Web OntologiesUses Cases of Web Ontologies

• Web portal • Multimedia collections • Corporate web site management • Design documentation • Agents and services • Ubiquitous computing


An Architecture of An Architecture of Semantic Community Web Portals

(From: http://www9.org/w9cdrom/134/134.html)

SesameSesame

A generic Architecture for Storing and Querying RDF and RDF SchemaA generic Architecture for Storing and Querying RDF and RDF Schema


What is Sesame ?What is Sesame ?

Sesame is RDF Schema-based repository

and querying facility that offers:– persistent storage of RDF data

– export of repository contents in RDF format

– data administration functionality

– query engine (RQL , SeRQL)


Sesame’s ArchitectureSesame’s Architecture


The RQL Query ModuleThe RQL Query Module• The Query Module follows the path when handling a query.


The Admin ModuleThe Admin Module

• Two main functions :– Incrementally adding RDF data/schema information.– Clearing a repository.

• The Parser delivers the information to the admin module on a per-statement basis : (S , P , O) .

• The admin subsequently checks each statement for consistency with the information already present in the repository , and infers implied information if necessary , as follow:


The Admin Module(2)The Admin Module(2)

• If P equals type , then the admin infers that O must be a class.

• If P equals subClassOf , then the admin infers that both S and O are classes.

• If P equals subPropertyOf , then admin infers that both S and O are properties.

• If P equals domain or range , the admin infers that S must be a property and O must be a class.


The RDF Export ModuleThe RDF Export Module

• Exports data in RDF format- Output contains actual contents of repository, query engine

outputs query results


RQL (RDF Query Language)RQL (RDF Query Language)

• Based on OQL (standard QL for object-relational DBMS)– Set of core queries

• Class, Property, subClassOf, …– Filters

• Select-from-where– Boolean expressions– Functional composition of queries

• Path expressions– For navigating the RDF model– Allowing bridging between RDF data and schema information

KA2 KA2 An Ontology-Based Community Web PortalAn Ontology-Based Community Web Portal


KA2KA2

• Knowledge Annotation Initiative of the Knowledge Acquisition Community

• The basic scenario– WWW documents of the KS community were annotated

according to the schema of an ontology.– The annotations enable intelligent access to these

documents and infer implicit knowledge from explicitly stated facts and rules from the ontology.

The KA2 OntologyThe KA2 Ontology

Class hierarchyPerson Employee Academic-Staff Lecturer Researcher Administrative-Staff Secretary Technical-Staff Student Phd-Student

RelationsAddress, Affiliation, Cooperates-With, Editor-Of,Email, First-Name, Has-Publication, Head-Of-Group, Head-Of-Project, Last-Name, Member-Of-Organization, Member-Of-Program-Committee, Member-Of-Research-Group, Middle-Initial, Organizer-Of-Chair-Of, Person-Name, Photo, Research-Interest, Secretary-Of, Studies-At, Supervises, Supervisor, Works-At-Project

Person-ontologyClass hierarchyOn-Line-PublicationPublication Article Article-In-Book Conference-Paper Journal-Article Technical-Report Workshop-Paper Book Journal IEEE-Expert IJHCS Special-Issue

RelationsAbstract, Book-Editor, Conference-Proceedings-Title, Contains-Article-In-Book, Contains-Article-In-Journal, Describes-Project, First-Page, Has-Author, Has-Publisher, In-Book, In-Conference, In-Journal, In-Organization,In-Workshop, Journal-Editor, Journal-Number, Journal-Publisher, Journal-Year, Last-Page, On-Line-Version, …

Publication-ontology


Accessing the Community Web PortalAccessing the Community Web Portal

• Query capability– In F-Logic mechanism

• Navigating capability– As the easy-to-use front-end of the query mechanism


Providing InformationProviding Information

• Integrating various syntactic and semantic formats based on the common ontology

• Three different modes of information provision are supported– Metadata-based information– Wrapper-based information– Fact-based information


Development of Web PortalsDevelopment of Web Portals


SummarySummary

• Semantic Web technology– Metadata – Facilitate interoperability at semantic level– Relieve the problem of information explosion– Enable the knowledge management