Introduction to Semantic Web Portal

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

Tatung Universitychingyeh@cse.ttu.edu.tw

http://www.cse.ttu.edu.tw/chingyeh

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Content

• Background• XML, XML Protocol and Web Services• EB Standard: RosettaNet• EB Standard: ebXML• Semantic Web: Machine Processable Web• Ontology Basics• XML-based Ontology Languages: RDFS, DAML, OWL• DAML-S: an Ontology for Semantic Web Services• Semantic Web Portals• Conclusions

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Background

• WWW– HTML

– HTTP

– Mainly man-machine interaction

• Electronic Business (EB)– Standard XML document

– XML Protocol

– AP-2-AP interaction

• Semantic Web Services– RDF

– Ontology

– Web Services, agents

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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

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XML Standards

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

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XML Protocol: SOAP

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<?xml version=“1.0” encoding=“UTF-8”?><SOAP:Encelope xmlns:SOAP=http://schemas.xmlsoap.org/soap/envelope xmlns=“http://www.smallco.org/order” xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance”> <SOAP:Header> <msg:MessageHeader xmlns:msg=“http://www.sterlingcommerce.com/message”> <msh:From>SterlingVommerce</msg:From> <msg:To>SmallCo</msg:To> <msg:Service>Purchase</msg:Service> <msg:Action>Order</msg:Action> <msg:MessageId>bbc006751</msg:MessageId> </msg:MessageHeader> </SOAP:Header> <SOAP:Body> <PurchaseOrder SOAP:encodingStyle=http://schemas.xmlsoap.org/soap/encoding/”> <PartnerID> <Name>Small Co Enterprise</Name> <ID type=“D-U-N-S+4”>123456789-0456</ID> </PartnerID> <Contact>John Adams</Contact> <Telephone>214-340-1234</Telephone> <Order> … </Order> <ShipInfo> … </ShipInfo> </PurchaseOrder> </SOAP:Body> </SOAP:Envelope>

A SOAP Message

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Web Services

Serviceregistry

Servicerequester

Serviceprovider

FindWSDL, UDDI

PublishWSDL, UDDI

Bind

Servicedescriptions

Servicedescriptions

Services

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Introduction to Semantic Web

• Facilities to put machine-understandable data on the Web are becoming a high priority for many communities.

• The Web can reach its full potential only if it becomes a place where data can be shared and processed by automated tools as well as by people.

• For the Web to scale, tomorrow's programs must be able to share and process data even when these programs have been designed totally independently.

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Introduction to Semantic 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

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The 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

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The Big Picture of SW

Ontology Basics

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Why Develop an Ontology

• Reasons why developing an ontology:– To share common understanding of the structure of

information among people or software agents– To enable reuse of domain knowledge– To make domain assumptions explicit– To separate domain knowledge from the operational

knowledge– To analyze domain knowledge

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Ontologies

• One widely cited definition of an ontology is Gruber’s [Gruber 1993] “A specification of a conceptualization”.

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Ontologies

• Ontologies can be used to provide a concrete specification of term names and term meanings.

What is an Ontology?What is an Ontology?

Catalog/ID

GeneralLogical

constraints

Terms/glossary

Thesauri“narrower

term”relation

Formalis-a

Frames(properties)

Informalis-a

Formalinstance

Value Restrs.

Disjointness, Inverse, part-

of…

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What Is in an Ontology?

• For the purposes of this guide an ontology is a formal explicit description of – concepts in a domain of discourse (classes (sometimes

called concepts)), – properties of each concept describing various features and

attributes of the concept (slots (sometimes called roles or properties)), and

– restrictions on slots (facets (sometimes called role restrictions)).

• An ontology together with a set of individual instances of classes constitutes a knowledge base.

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A Simple Knowledge-Engineering Methodology

• There is no one “correct” way or methodology for developing ontologies.

• Here we discuss general issues to consider and offer one possible process for developing an ontology.

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A Simple Knowledge-Engineering Methodology

Step 1: Determine the domain and scope of the ontology

Step 2: Consider reusing existing ontologies

Step 3: Enumerate important terms in the ontology

Step 4: Define the classes and the class hierarchy

Step 5: Define the properties of classes—slots

Step 6: Define the facets of the slots

Step 7: Create instances

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Uses Cases of Web Ontologies

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

XML-Based Ontology Languages

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RDF 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)

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RDF 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

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A 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

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EmailName

s:Creator

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

Another Example

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

Person://fi/654645635

Ora Lassila lassila@w3.org

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Example: 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

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rdf:_1

rdf:_2

rdf:_3

rdf:typesource

ftp.eu.net

ftp.cs.purdue.edu

ftp.x.org

Example: 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

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RDF Syntax I

• Data model does not enforce particular syntax• Specification suggests many different syntaxes

based on XML• General form:

<rdf:RDF> <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator>Ora Lassila</s:Creator> <s:createdWith rdf:resource=“http://www.w3c.org/amaya”/> </rdf:Description></rdf:RDF>

Starts an RDF-Description

Properties

Subject (OID)

Literal

Resource (possibly another RDF-description)

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Resulting Graph

<rdf:RDF> <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator>Ora Lassila</s:Creator> <s:createdWith rdf:resource=“http://www.w3c.org/amaya”/> </rdf:Description></rdf:RDF>

http://www.w3c.org/amaya

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

Ora Lassila

s:createdWiths:Creator

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RDF Syntax II: Syntactic Varieties

<s:Homepage rdf:about="http://www.w3.org/Home/Lassila” s:Creator=“Ora Lassila”/>

<s:createdWith> <s:HTMLEditor rdf:about=“http://www.w3c.org/amaya”/> </s:createdWith> </s:Homepage>

Typing InformationIn-Element Property

Property

Subject (OID)

http://www.w3c.org/amaya

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

Ora Lassila

s:createdWiths:Creator

HTMLEditor

s:Homepagerdf:type

rdf:type

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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.

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Most 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)

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DAML+OIL: an Ontology Language

• Extension of RDF Schema• Ontology Language DAML+OIL: Result of a Joint

(European + US-American) Committee• Extension of RDF Schema

– Class Expressions (Intersection, Union, Complement)– XML Schema Datatypes– Enumerations– Property Restrictions

• Cardinality Constraints

• Value Restrictions

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OWLW3C Web Ontology Language

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

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OWLW3C 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

DAML-S: An Ontology for Semantic web Service

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DAML-S

• Users and software agents should be able to discover, invoke, compose, and monitor Web resources offering particular services and having particular properties.

• As part of the DARPA Agent Markup Language program, we have begun to develop an ontology of services, called DAML-S.

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Top Level of the Service Ontology

Service

Resource

ServiceGrounding

ServiceProfile

ServiceModel

provides presents

supports described by

(what it does)

(how it works)(how to access it)

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Process Modeling Ontology

Semantic Web Portal

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Web Portals

• A web portal is a web site that provides information content on a common topic.– General portals, e.g., Yahoo, Excite, Netscape, Lycos,

CNET, MSN, and AOL.com– Specialized portal e.g., gardeners.com, semanticweb.org

• Making valuable information to be found– directory service, – search facility– news, e-mail, – community forum

KA2 An Ontology-Based Community Web Portal

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Ontology-Based Web Portals

• Ontology represents– common knowledge and interests sharing within their

community

• Tasks that ontology can be used to support a portal– Accessing a portal

• Conceptual search and navigation

• Inference capabilities

– Providing information• Methods and tools accounting for the diversity of information

sources

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KA2

• 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.

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The 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

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Accessing the Community Web Portal

• Query capability– In F-Logic mechanism

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

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Development of Web Portals

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The System Architecture

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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)

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Sesame’s Architecture

Web server

Web server

Web server

Web server

Content providers

User User User User

Ontology Knowledgewarehouse

Portal

Annotator Wrapper

Discovery Use Tailoring Social

Inference engine

An Ontology-Based Portal for Digital LibraryServices

System Architecture

DAML、 KA2Domain

Ontology lib

User require Ontology(RDFS、 DAML)

Annotatortools

KnowledgeWarehouse

(RDF)

Transtrator(RDFS to Flex)

Translator(RDF to Flex)

Flex instancestore

Schema-in-Flexstore

KnowledgeWarehouse

(RDF)

RDF

Document

AnnotationProgram

RDF metadata

Profilemanagement

Conceptionsearch

NLP search

Ontology

Domainspecific user

General user

Flexinference engine

Contentprovider

Translator ( RDF To FLEX)

Ontology-Based Web Portal(1/2)

Ontology-Based Web Portal(2/2)

Annotation Tool

57

58

59

60

61

Current work(2/3)

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Conclusions

• New web technologies– XML– Electronic Business– Semantic Web (Services)

• Integration of existing technologies to create new one