Introduction to Semantic Web Portal
Ching-Long Yeh 葉慶隆Department of Computer Science and Engineering
Tatung [email protected]
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 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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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
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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 [email protected]
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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
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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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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
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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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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)
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