An Introduction to Semantic Web Portal
Ching-Long Yeh
葉慶隆
Department of Computer Science and Engineering
Tatung University
chingyeh@cse.ttu.edu.tw
http://www.cse.ttu.edu.tw/chingyeh
Outline
•
•
•
•
•
A brief description to the Semantic Web Portal
Architectural basis of the Semantic Web
KA2: an ontology-based web portal
An architecture of RDF triple data store
Conclusions
Semantic Web Portal
2
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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3
Introduction to Semantic Web
• The Semantic Web is a vision:
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
• See “W3C Semantic Web Activity,” by Marja-Riitta Koivunen, for
more descriptions.
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4
The Semantic Web Layered Architecture
Proof
Proof
Tim Berners-Lee:
“Axioms, Architecture and
Aspirations”
W3C all-working group
plenary Meeting
28 February 2001
(http://www.w3.org/2001/T
alks/0228-tbl/slide5-0.html)
Logic
Rules
Ontology
Sig
RDF Schema
RDF M&S
XML Schema
XML
URI
Semantic Web Portal
Namespaces
Unicode
5
AI’s Chance
Namespaces
• Increasing demand
for formalized
knowledge on the
Web: AI’s chance!
• XML- & RDF-based
markup languages
provide a 'universal'
storage/interchange
format for such Webdistributed knowledge
representation.
CSS
DTDs
XSLT
DAML
Stylesheets
Agents
Ontobroker
HornML
RuleML
Rules
Transformations
XML
XQL
Queries
XQuery
XML-QL
SHOE
Frames
RDF[S]
Acquisition
TopicMaps
Protégé
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6
The Big
Picture of SW
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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8
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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Introduction to XML-Based Ontology
Proof
Proof
Logic
Rules
Ontology
Sig
RDF Schema
RDF M&S
XML Schema
XML
URI
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Namespaces
Unicode
10
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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11
Namespace Bindings
• Prefixes are bound to namespace URIs by attaching an
xmlns:prefix attribute to the prefixed element or one of its
ancestors, prefix:name1 ,..., prefix:namen
• The value of the xmlns:prefix attribute is a URI, which
may or (unlike for DTDs!) may not point to a description
of the namespace’s syntax
• An element can use bindings for multiple name-spaces
via attributes xmlns:prefix1 ,..., xmlns:prefixm
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XML Document Instance and DTD
<mail:address xmlns:mail="http://www.deutschepost.de/"
xmlns:tele="http://www.telekom.de/">
<mail:name>Xaver M. Linde</mail:name>
<mail:street>Wikingerufer 7</mail:street>
<mail:town>10555 Berlin</mail:town>
<mail:bill>12.50</mail:bill>
<tele:phone>030/1234567</tele:phone>
<tele:phone>030/1234568</tele:phone>
<tele:fax>030/1234569</tele:fax>
<tele:bill>76.20</tele:bill>
<!ELEMENT address (name, street, town,
</ mail:address>
bill, phone+, fax+, bill)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT street (#PCDATA)>
<!ELEMENT town (#PCDATA)>
<!ELEMENT bill (#PCDATA)>
<!ELEMENT phone (#PCDATA)>
<!ELEMENT fax (#PCDATA)>
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<!ELEMENT ARTIST (#PCDATA)>
XML Schema
• An XML syntax that's an alternative and/or
supplement to DTDs
• Data typing of element and attribute content
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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)
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
– Property
– Value
(subject)
http://www.w3.org/Home/Lassila
(predicate) http://www.schema.org/#Creator
(object)
"Ora Lassila”
• Directed graph
s:Creator
Ora Lassila
http://www.w3.org/Home/Lassila
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Another Example
• To add properties to Creator, point through an
intermediate Resource.
http://www.w3.org/Home/Lassila
s:Creator
Person://fi/654645635
Name
Ora Lassila
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Email
lassila@w3.org
18
Example: Bag
•
The students in
course 6.001
are Amy, Tim,
John, Mary,
and Sue
/courses/6.001
Rdf:Bag
rdf:type
/Students/Amy
students
rdf:_1
rdf:_2
bagid1
/Students/Tim
rdf:_3
/Students/John
rdf:_4
rdf:_5
/Students/Mary
/Students/Sue
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Example: Alternative
• The source code for X11 may be found at ftp.x.org,
ftp.cs.purdue.edu, or ftp.eu.net
http://x.org/package/X11
rdf:Alt
rdf:type
source
altid
rdf:_1
ftp.x.org
rdf:_2
ftp.cs.purdue.edu
rdf:_3
ftp.eu.net
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RDF Syntax I
• Data model does not enforce particular syntax
• Specification suggests many different syntaxes
based on XML
• General form:Starts an RDF-Description
Subject (OID)
<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>
Literal
Properties
Resource (possibly another RDF-description)
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Resulting Graph
http://www.w3.org/Home/Lassila
s:createdWith
s:Creator
http://www.w3c.org/amaya
Ora Lassila
<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>
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RDF Syntax II: Syntactic Varieties
Typing Information
Subject (OID)
In-Element Property
<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>
rdf:type
Property
s:Homepage
http://www.w3.org/Home/Lassila
s:Creator
s:createdWith
rdf:type
Ora Lassila
http://www.w3c.org/amaya
HTMLEditor
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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Example: Intersection & Synonyms
<daml:Class rdf:ID="TallMan">
<daml:intersectionOf rdf:parseType="daml:collection">
<daml:Class rdf:about="#TallThing"/>
<daml:Class rdf:about="#Man"/>
</daml:intersectionOf>
</daml:Class>
<daml:Class rdf:ID="HumanBeing">
<daml:sameClassAs rdf:resource="#Person"/>
</daml:Class>
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27
Example: Disjoint & Complement
<daml:Disjoint rdf:parseType="daml:collection">
<daml:Class rdf:about="#Car"/>
<daml:Class rdf:about="#Person"/>
<daml:Class rdf:about="#Plant"/>
</daml:Disjoint>
Disjoint not strictly necessary, since expressible via pairwise subClassOf
of complementOf, as for Car and Person:
<daml:Class rdf:ID="Car">
<rdfs:comment>no car is a person</rdfs:comment>
<rdfs:subClassOf>
<daml:Class>
<daml:complementOf rdf:resource="#Person"/>
</daml:Class>
</rdfs:subClassOf>
</daml:Class>
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Example: Properties
(Transitive, Inverse, subProperty, UniqueProperty, range, Datatypes)
<daml:TransitiveProperty rdf:ID="hasAncestor"/>
<daml:ObjectProperty rdf:ID="hasChild">
<daml:inverseOf rdf:resource="#hasParent"/>
</daml:ObjectProperty>
<daml:UniqueProperty rdf:ID="hasMother">
<rdfs:subPropertyOf rdf:resource="#hasParent"/>
<rdfs:range rdf:resource="#Female"/>
</daml:UniqueProperty>
<daml:DatatypeProperty rdf:ID="age">
<rdf:type rdf:resource="http://www.daml.org/2001/03/daml+oil#UniqueProperty"/>
<rdfs:range rdf:resource="http://www.w3.org/.../XMLSchema#nonNegativeInteger"/>
</daml:DatatypeProperty>
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Using User-defined Datatypes
(based on XML Schema)
<xsd:simpleType name="over17">
<!--over17 is an XMLS datatype based on decimal-->
<!--with the added restriction that values must be >=18-->
<xsd:restriction base="xsd:decimal">
<xsd:minInclusive value="18"/>
</xsd:restriction>
</xsd:simpleType>
<daml:Class rdf:ID="Adult">
<daml:intersectionOf rdf:parseType="daml:collection">
<daml:Class rdf:about="#Person"/>
<daml:Restriction>
<daml:onProperty rdf:resource="#age"/>
<daml:hasClass rdf:resource="somefile#over17"/>
</daml:Restriction>
</daml:intersectionOf>
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</daml:Class>
Instances (Individuals)
<daml:Class rdf:ID="Person">
. . .
</daml:Class>
<Person rdf:ID="Adam">
<rdfs:label>Adam</rdfs:label>
<rdfs:comment>Adam is a person.</rdfs:comment>
<age><xsd:integer rdf:value="13"/></age>
<shoesize>
<xsd:decimal rdf:value="9.5"/>
</shoesize>
</Person>
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Web Services
Service
descriptions
Service
registry
Find
Publish
WSDL, UDDI
Service
requester
WSDL, UDDI
Bind
Service
provider Services
Service
descriptions
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32
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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33
Top Level of the Service Ontology
Resource
provides
presents
ServiceProfile
(what it does)
Service
(how to access it)
supports
(how it works)
described by
Service
Grounding
ServiceModel
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Process Modeling Ontology
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35
Concept of ebXML Business
Process Specification Schema
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36
Business
Process
Specification
in XML
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37
KA2
An Ontology-Based Community Web Portal
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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39
The KA2 Ontology
Person-ontology
Class hierarchy
Person
Employee
Academic-Staff
Lecturer
Researcher
Administrative-Staff
Secretary
Technical-Staff
Student
Phd-Student
Relations
Address, Affiliation, Cooperates-With,
Editor-Of,Email, First-Name, HasPublication, Head-Of-Group, Head-OfProject, Last-Name, Member-OfOrganization, Member-Of-ProgramCommittee, Member-Of-Research-Group,
Middle-Initial, Organizer-Of-Chair-Of,
Person-Name, Photo, Research-Interest,
Secretary-Of, Studies-At, Supervises,
Supervisor, Works-At-Project
Publication-ontology
Class hierarchy
On-Line-Publication
Publication
Article
Article-In-Book
Conference-Paper
Journal-Article
Technical-Report
Workshop-Paper
Book
Journal
IEEE-Expert
IJHCS
Special-Issue
Relations
Abstract, Book-Editor, ConferenceProceedings-Title, Contains-Article-InBook, Contains-Article-In-Journal,
Describes-Project, First-Page, HasAuthor, Has-Publisher, In-Book, InConference, In-Journal, In-Organization,
In-Workshop, Journal-Editor, JournalNumber, Journal-Publisher, Journal-Year,
Last-Page, On-Line-Version, …
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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41
Query Capabilities
For all publications of the researcher “Steffen Staab”.
FORALL Pub <EXISTS ResID ResID:Researcher[NAME->> Steffen "Staab";
PUBLICATION ->> Pub].
Two researchers cooperate,
if a Researcher X works at a Project Proj and
if a Researcher Y works at the same Project Proj and
X is another person than Y
FORALL X; Y; Proj
X:Researcher[COOPERATESWITH ->> Y:Researcher]
<X:Researcher[WORKSATPROJECT->>Proj:Project]
AND
Y:Researcher[WORKSATPROJECT->>Proj:Project]
AND NOT equal(X; Y ):
Which researchers are cooperating with other r?
FORALL ResID1, ResID2 <ResID1:Researcher[COOPERATESWITH
->> ResID2].
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Navigating and Querying the Portal
• Query the portal using F-Logic is too inconvenient.
• Navigating and querying the web
– A hypertext link may contain a query dynamically evaluated
when clicking on the link (See P. 45)
– Query generated by using the hyperbolic view interface (See
P. 46)
– Queries may be personalized and for the different users and
available for the user in a selection list.
– An expert mode: Querying the portal by typing an F-Logic
statement
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Providing 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
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46
Metadata-based Information
In RDF, XML
Metadata
Information
source
Annotation tool
(OntoPad Annotea, …)
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47
Wrapper-based Information
• Annotating information sources by hand is timeconsuming.
Semi-structured
Information sources
(e.g., HTML)
Structured
Information sources
(e.g., RDB)
Wrapper
program
Metadata
(Onto Wrapper)
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48
Fact-Based Information
New facts
Knowledge
warehouse
create
add,
modify,
delete
Fact Editor
(Ontoedit, OilED,
Protégé 2000)
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49
Development of Web Portals
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50
The System Architecture
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An Architecture of
RDF Triple Data
Store
API's
(in Prolog
and SQL)
User
interface
Crawler
Triples in Prolog
and RDB tables
RDF
parser and
generator
RDF documents
Editing and Annotation
RDF Parser and Generator
• Using DCG in Prolog as the development tool
• Formal grammar in RDF M&S Spec
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/#grammar
Formal grammar
rules in DCG
Prolog’s
working storage
Prolog’s
inference engine
Semantic Web Portal
User
interface
53
[6.1] RDF
[6.2] obj
[6.3] description
[6.4] container
::= ['<rdf:RDF>'] obj* ['</rdf:RDF>']
::= description | container
::= '<rdf:Description' idAboutAttr? bagIdAttr? propAttr* '/>'
| '<rdf:Description' idAboutAttr? bagIdAttr? propAttr* '>'
propertyElt* '</rdf:Description>'
| typedNode
::= sequence | bag | alternative
rdf(Objs) -->
(['<?'],
([nm/'xml'];[nm/'XML'];
[nm/'xmls'];[nm/'XMLS']),
([nm/'version','=',qs/_];[]),
([nm/'encoding','=',qs/_];[]),
['?>'],{wl('XML heading')}
;[]),
(fullSTG('RDF',NS)
;
halfSTG('RDF',NS),
['>']
;
[ ]),
objStar(Objs),
(fullETG('RDF',NS);[ ]).
objStar(Out) -->
obj(O),
objStar(R),{Out=[O|R]}
;
[],{Out=[]}.
obj(Obj) -->
container(Obj)
;
description(_),{getAllTriples(Obj)}.
getAllTriples(Obj):findall(statement(A,B,C),statement(A,B
,C),Obj).
description(_) -->
halfSTG('Description',NS),
(idAboutAttr(IdAboutAttr);[]),
(bagIdAttr(BagIdAttr);[]),
propAttrStar(IdAboutAttr),
(['/>']
;
['>'],
propertyEltStar(IdAboutAttr),
fullETG('Description',NS)),
{reificationOfStatements(IdAboutAttr,B
agIdAttr)}
;
typedNode.
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://purl.org/metadata/dublin_core#">
<rdf:Description about="http://www.foo.com/cool.html">
<dc:Creator>
<rdf:Seq ID="CreatorsAlphabeticalBySurname">
<rdf:li>Mary Andrew</rdf:li>
<rdf:li>Jacky Crystal</rdf:li>
</rdf:Seq>
</dc:Creator>
<dc:Identifier>
<rdf:Bag ID="MirroredSites">
<rdf:li rdf:resource="http://www.foo.com.au/cool.html"/>
<rdf:li rdf:resource="http://www.foo.com.it/cool.html"/>
</rdf:Bag>
</dc:Identifier>
<dc:Title>
<rdf:Alt>
<rdf:li xml:lang="en">The Coolest Web Page</rdf:li>
<rdf:li xml:lang="it">Il Pagio di Web Fuba</rdf:li>
</rdf:Alt>
</dc:Title></rdf:Description></rdf:RDF>
RDF input
[statement(about/http://www.foo.com/cool.html,
Title,
alt(_87882,[string/The Coolest Web Page,
string/Il Pagio di Web Fuba])),
statement(about/http://www.foo.com/cool.html,
Identifier,
bag(id/MirroredSites,[resource/http://www.foo.com.au/cool.html,
resource/http://www.foo.com.it/cool.html])),
statement(about/http://www.foo.com/cool.html,
Creator,
seq(id/CreatorsAlphabeticalBySurname,[string/Mary Andrew,
string/Jacky Crystal]))]
Prolog
output
RDF Statements in RDB Tables
RDF_NameSpace
Id
1
2
…
NsName
http://www.w3.org/2000/01/rdf#
http://purl.org/metadata/dublin_core#
…
RDF_Resource
Id
1
2
…
ResourceName
http://www.dlib.org
http://www.foo.com
…
RDF_Predicate
Id
1
2
…
NS
2
2
…
PredicateName
Creator
Language
…
RDF_Literal
Id
1
2
…
LiteralName
Jacky Crystal
English
…
RDF_Statement
Id
1
2
…
Resource
1
1
…
Predicate
1
2
…
Literal
1
2
…
User Interface
Conceptual Search
• Natural language interface is the best choice, but is
very difficult to obtain a good result.
• Form-based interface is easy to implement, but is too
restricted.
• Hierarchical directory browsing is perhaps a good
idea, if the domain in question is well organized.
• We also propose a frame-based query interface.
target_concept[(attribute1[:value1], …)]
teacher(office:6th_floor)
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User Interface
Natural Language Generation
Content
extraction
Knowledge
Warehouse
(RDF)
Text
planning
Content
planning
Multi-sentential
text
NLG
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58
Future Work
• Building an ontology for the Digital Archive Services
– Consisting of resource and process parts
• Declarative approach to semantic web service
– Using an workflow engine to interpret the process
descriptions
• Intelligent Q&A for digital archive
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Summary
• Semantic Web portals
– Machine-understandable information
– RDF store
– Accessing information
• Navigation and query
– Providing information
• Annotation, wrapper, fact editing
– Enabling automatic processing by software agents
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