design and implementation of an rdf data store

Design and Implementation of An RDF Data Store

Ching-Long Yeh 葉慶隆Department of Computer Science and EngineeringTatung UniversityEmail: [email protected]: httP://www.cse.ttu.edu.tw/chingyeh

An RDF Data Store 2

OutlineOutline

• Introduction to the Semantic Web• Semantic Web Layered Architecture:

– XML, RDF(S), DAML(-S)

• The Big Picture of the Semantic Web• An Architecture of RDF Triple Data Store

– An RDF Parser in Prolog– The Repository storage– APIs and User Interface

• Semantic Community Portal• Future Work and Conclusions

An RDF Data Store 3

SourcesSources

• Part of the slides are selected from the following sources:– Knowledge Markup and Resource Semantics, By

Harold Boley, Stefan Decker, and Michael Sintek, IJCAI-01 Tutorial, http://www.ijcai-01.org/

– Anupriya Ankolenkar, et al., “DAML-S: Semantic Markup For Web Services,”, Proceedings of SWWS’ 01, the First Semantic Web Working Symposium, California, USA, July 30 - August 1, 2001.

An RDF Data Store 4

Introduction to Semantic WebIntroduction 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.

An RDF Data Store 5

Introduction to Semantic WebIntroduction 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.

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

An RDF Data Store 6

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

An RDF Data Store 7

AI’s ChanceAI’s Chance

• Increasing demand for formalized knowledge on the Web: AI’s chance!

• XML- & RDF-based markup languages provide a 'universal' storage/interchange format for such Web-distributed knowledge representation.

DTDs

XML

RDF[S]

Namespaces

Stylesheets

CSS

XSLT

XQL

Queries

XML-QL

Transformations

Acquisition

Protégé

Agents

Frames

Rules

SHOE

HornML

RuleML

DAML

XQuery

TopicMaps

Ontobroker

XML FundamentalsXML Fundamentals

Source: http://www.ibiblio.org/xml/slides/sd2001east/fundamentals/XML_Fundamentals.html

An RDF Data Store 9

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

An RDF Data Store 10

Extensible Markup LanguageExtensible Markup Language

• Language – It has a grammar– It has a vocabulary (sort of)– It can be parsed by machines

• Markup Language– It says what things are; not what they do– It is not a programming language– It is not compiled

• Extensible – You can add words to the language


XML is a Meta Markup LanguageXML is a Meta Markup Language

• Not like HTML, troff, LaTeX• Make up the tags you need as you need them• The tags you create can be documented in a

Document Type Definition (DTD)• A meta syntax for domain-specific markup

languages like MusicML, MathML, and XHTML


XML ApplicationsXML Applications

• A specific markup language that uses the XML meta-syntax is called an XML application

• Different XML applications have their own more constricted syntaxes and vocabularies within the broader XML syntax

• Further syntax can be layered on top of this; e.g. data typing through schemas


XML describes structure and XML describes structure and semantics, not formattingsemantics, not formatting

• XML documents form a tree– Document Object Model (DOM)

• Element and attribute names reflect the kind of the element– DTD, Schema

• Formatting can be added with a style sheet– Cascading Style Sheets (CSS)– Extensible Stylesheet language (XSL)


XML HypertextXML Hypertext

• A Uniform Resource Identifier (URI) names or locates a resource

• An XLink defines connections between two or more documents identified by URIs

• XPath identifies particular nodes within a document

• An XPointer adds an XPath to a URI• XBase defines the URI against which relative

URIs are resolved • XInclude embeds a document identified by a

URI inside an XML document.


A Song Description in HTMLA Song Description in HTML

<dt>Hot Cop<dd> by Jacques Morali, Henri Belolo, and Victor Willis<ul><li>Producer: Jacques Morali<li>Publisher: PolyGram Records<li>Length: 6:20<li>Written: 1978<li>Artist: Village People</ul>


A Song Description in XMLA Song Description in XML

<SONG> <TITLE>Hot Cop</TITLE> <COMPOSER>Jacques Morali</COMPOSER> <COMPOSER>Henri Belolo</COMPOSER> <COMPOSER>Victor Willis</COMPOSER> <PRODUCER>Jacques Morali</PRODUCER> <PUBLISHER>PolyGram Records</PUBLISHER> <LENGTH>6:20</LENGTH> <YEAR>1978</YEAR> <ARTIST>Village People</ARTIST></SONG>


Style Sheets Provide FormattingStyle Sheets Provide Formatting(CSS)(CSS)

SONG {display: block; font-family: New York, Times New Roman, serif}TITLE {display: block; font-size: 24pt; font-weight: bold; font-family: Helvetica, sans}COMPOSER {display: block}PRODUCER {display: block}YEAR {display: block}PUBLISHER {display: block}LENGTH {display: block}ARTIST {display: block; font-style: italic}


Attaching Style Sheets to DocumentsAttaching Style Sheets to Documents

<?xml-stylesheet type="text/css" href="song.css"?><SONG> <TITLE>Hot Cop</TITLE> <COMPOSER>Jacques Morali</COMPOSER> <COMPOSER>Henri Belolo</COMPOSER> <COMPOSER>Victor Willis</COMPOSER> <PRODUCER>Jacques Morali</PRODUCER> <PUBLISHER>PolyGram Records</PUBLISHER> <LENGTH>6:20</LENGTH> <YEAR>1978</YEAR> <ARTIST>Village People</ARTIST></SONG>


An XSLT Stylesheet (Part 1)An XSLT Stylesheet (Part 1)

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/"> <html> <head><title>Song</title></head> <body> <xsl:apply-templates select="SONG"/> </body> </html> </xsl:template>


An XSLT Stylesheet (Part 2)An XSLT Stylesheet (Part 2) <xsl:template match="SONG"> <h1> <xsl:value-of select="TITLE"/> by the <xsl:value-of select="ARTIST"/> </h1> <ul> <li>Length: <xsl:value-of select="LENGTH"/></li> <li>Producer: <xsl:value-of select="PRODUCER"/></li> <li>Publisher: <xsl:value-of select="PUBLISHER"/></li> <li>Year: <xsl:value-of select="YEAR"/></li> <xsl:apply-templates select="COMPOSER"/> </ul> </xsl:template>

<xsl:template match="COMPOSER"> <li>Composer: <xsl:value-of select="."/></li> </xsl:template></xsl:stylesheet>


Transforming the DocumentTransforming the Document<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Song</title> </head> <body> <h1>Hot Cop by the Village People </h1> <ul> <li>Length: 6:20</li> <li>Producer: Jacques Morali</li> <li>Publisher: PolyGram Records</li> <li>Year: 1978</li> <li>Composer: Jacques Morali</li> <li>Composer: Henri Belolo</li> <li>Composer: Victor Willis</li> </ul> </body></html>

XSLT Processor

(IE 5)

XSL document(template rules)

XML document

Output

A DTD for SongsA DTD for Songs

<!ELEMENT SONG (TITLE, COMPOSER+, PRODUCER*, PUBLISHER*, LENGTH?, YEAR?, ARTIST+)>

<!ELEMENT TITLE (#PCDATA)>

<!ELEMENT COMPOSER (#PCDATA)><!ELEMENT PRODUCER (#PCDATA)><!ELEMENT PUBLISHER (#PCDATA)><!ELEMENT LENGTH (#PCDATA)><!ELEMENT YEAR (#PCDATA)>

<!ELEMENT ARTIST (#PCDATA)>


Well-formednessWell-formedness

• Rules:– Open and close all tags– Empty tags end with />– There is a unique root element– Elements may not overlap– Attribute values are quoted– < and & are only used to start tags and entities– Only the five predefined entity references are used– Plus more...


ValidityValidity

• To be valid an XML document must be1. Well-formed2. Must have a Document Type Definition

(DTD)3. Must comply with the constraints specified

in the DTD


What Is XML Used for?What Is XML Used for?

• Domain-Specific Markup Languages– XML in industrial applications:

http://www.xml.org/xml/industry_industrysectors.jsp

• Self-Describing Data– Much data is lost due to format problems.

• Interchange of Data Among Applications– Electronic business: RosettaNet, ebXML


XML NamespacesXML Namespaces

• XML namespaces are akin to namespaces, packages, and modules in programming languages

• Disambiguation of tag–and attribute–names from different XML applications (“spaces”) through different prefixes

• A prefix is separated from the local name by a “:”, obtaining prefix:name tags

• Namespaces constitute a layer on top of XML 1.0, since prefix:name is again a valid tag name and namespace bindings are ignored by some tools


Namespace BindingsNamespace 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


Two-Namespace Example:Two-Namespace Example:Snail-Mail and Telecoms Address PartsSnail-Mail and Telecoms Address Parts

<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></ mail:address>

bill disambiguation through mail and tele prefixes

Introduction to RDFIntroduction to RDF• RDF (Resource Description Framework)

– Beyond Machine readable to Machine understandable

• RDF unites a wide variety of stakeholders:– Digital librarians, content-raters, privacy advocates,

B2B industries, AI...– Significant (but less than XML) industrial momentum,

lead by W3C

• 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)

Knowledge Markup and Resource Semantics, By Harold Boley, Stefan Decker, and Michael Sintek, IJCAI-01 Tutorial, http://www.ijcai-01.org/


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]


Collection ContainersCollection Containers

• Multiple occurrences of the same PropertyType don’t establish a relation between the values– The Millers own a boat, a bike, and a TV set– The Millers need (a car or a truck)– (Sarah and Bob) bought a new car

• RDF defines three special Resources:– Bag unordered values rdf:Bag

– Sequence ordered values rdf:Seq

– Alternative single value rdf:Alt• Core RDF does not enforce ‘set’ semantics amongst

values


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


Statements About StatementsStatements About Statements

• Making statements about statements requires a

process for transforming them into Resources

– subject the original resource

– predicate the original property

– object the original value

– type rdf:Statement



Ralph Swick says that Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila.

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:a="http://description.org/schema/"> <rdf:Description> <rdf:subject resource="http://www.w3.org/Home/Lassila" /> <rdf:predicate resource="http://description.org/schema/Creator" /> <rdf:object>Ora Lassila</rdf:object> <rdf:type resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /> <a:attributedTo>Ralph Swick</a:attributedTo> </rdf:Description></rdf:RDF>



rdf:Statement s:Creator

Ora Lasilla

Ralph Swick

rdf:object

rdf:predicate

a:attributedTo

rdf:type

rdf:subject

Representation of a reified statement



<rdf:RDF> <rdf:Description about="http://www.w3.org/Home/Lassila" bagID="D_001"> <s:Creator>Ora Lassila</s:Creator> <s:Title>Ora's Home Page</s:Title> </rdf:Description> <rdf:Description aboutEach="#D_001"> <a:attributedTo>Ralph Swick</a:attributedTo> </rdf:Description></rdf:RDF>


RDF Syntax IRDF 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)


Resulting GraphResulting 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


Ora Lassila

s:createdWiths:Creator

RDF Syntax II: Syntactic VarietiesRDF 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


Ora Lassila

s:createdWiths:Creator

HTMLEditor

s:Homepagerdf:type

rdf:type

RDF SchemaRDF Schema


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)

Classes and PropertiesClasses and Properties

Resources

Classes

Property

ConstraintProperty

•rdf:type•rdfs:subClassOf•rdfs:subPropertyOf•rdfs:comment•rdfs:label•rdfs:seeAlso•rdfs:isDefinedBy

•rdfs:domain•rdfs:range

•rdfs:Resource•rdfs:Class•rdf:Property•rdfs:ConstraintProperty•rdfs:Literal

Classes and Resources as Sets and Elements

DARPA Agent Markup LanguageDARPA Agent Markup LanguageDAMLDAML


DARPA Agent Markup Language DARPA Agent Markup Language ProgramProgram

• DARPA funded Research Program (also funded the Development of the ARPANNET -> Internet)

• Focusing on building the foundation for the Semantic Web: http://www.daml.org

• Ontology Language DAML+OIL: Result of a Joint (European + US-American) Committee

• Rule Language in preparation


DAML+OILDAML+OIL

• 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


Example: Intersection & SynonymsExample: 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>


Example: Disjoint & ComplementExample: 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>

<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>

Disjoint not strictly necessary, since expressible via pairwise subClassOfof complementOf, as for Car and Person:


Example: Properties Example: Properties (Transitive, Inverse, subProperty, UniqueProperty, range, (Transitive, Inverse, subProperty, UniqueProperty, range,

Datatypes)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>

Using User-defined DatatypesUsing User-defined Datatypes(based on XML Schema)(based on XML Schema)

<xsd:simpleType name="over17">  <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> </daml:Class>


Instances (Individuals)Instances (Individuals)

<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>

<daml:Class rdf:ID="Person"> . . .</daml:Class>

Semantic Web ServicesSemantic Web Services

Source: Anupriya Ankolenkar, et al., “DAML-S: Semantic Markup For Web Services,”, Proceedings of SWWS’ 01, the First Semantic Web Working Symposium, California, USA, July 30 - August 1, 2001


Web ServicesWeb Services

Serviceregistry

Servicerequester

Serviceprovider

FindWSDL, UDDI

PublishWSDL, UDDI

Bind

Servicedescriptions

Servicedescriptions

Services


What Is DAML-SWhat Is 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.


Some Motivating TasksSome Motivating Tasks

• Automatic Web service discovery• Automatic Web service invocation• Automatic Web service composition and

interoperation• Automatic Web service execution

monitoring


Top Level of the Service OntologyTop Level of the Service Ontology

Service

Resource

ServiceGrounding

ServiceProfile

ServiceModel

provide presents

supports

describedBy

(what it does)

(how it works)

(how to access it)


Process Modeling OntologyProcess Modeling Ontology

The Big The Big Picture of Picture of

SWSW


Editing and Annotation ToolsEditing and Annotation Tools

• Protégé-2000• OntoEdit • OilED• Amaya

An Architecture of RDF Triple Data Store

RDFparser andgenerator

Triples in Prologand RDB tables

RDF documentsCrawler

Userinterface

API's(in Prologand SQL)

Editing and Annotation


RDF Parser and GeneratorRDF 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

Prolog’s inference engine

Formal grammar rules in DCG

Prolog’s working storage

User interface

[6.1] RDF ::= ['<rdf:RDF>'] obj* ['</rdf:RDF>'][6.2] obj ::= description | container[6.3] description ::= '<rdf:Description' idAboutAttr? bagIdAttr? propAttr* '/>' | '<rdf:Description' idAboutAttr? bagIdAttr? propAttr* '>' propertyElt* '</rdf:Description>' | typedNode[6.4] container ::= 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,BagIdAttr)} ; typedNode.

[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]))]

<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

Prolog output

RDF Statements in RDB TablesRDF Statements in RDB Tables

Id NsName1 http://www.w3.org/2000/01/rdf#2 http://purl.org/metadata/dublin_core#… …

Id NS PredicateName1 2 Creator2 2 Language… … …

Id ResourceName1 http://www.dlib.org2 http://www.foo.com… …

Id LiteralName1 Jacky Crystal2 English… …

Id Resource Predicate Literal1 1 1 12 1 2 2… … … …

RDF_NameSpace

RDF_Predicate

RDF_Literal

RDF_Statement

RDF_Resource


Application Program InterfacesApplication Program Interfaces

• RDF Query language is syntactically verbose.

<rdfquery> <rdfq:From> <rdf:Bag> <li resource="http://www.research.ibm.com/people/ashok/paper1.html"/> <li resource="http://www.research.ibm.com/people/ashok/paper3.html"/> <li resource="http://www.research.ibm.com/people/neel/paper1.html"/> <li resource="http://www.research.ibm.com/people/neel/paper7.html"/> </rdf:Bag> </rdfq:From></rdfquery>

Selecting all resources from a collection


Application Program InterfacesApplication Program Interfaces

get_frame - retrieves attribute values for a frame

add_frame - adds or updates attribute values for a frame

del_frame - deletes attribute values from a frame

• We propose a set of frame-based APIs for programmers to access the RDF repository.


User InterfaceUser Interface

• 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)


Related WorkRelated Work

• Jena– HP Labs in Bristol, England– Jena is an API in the Java programming language, for

the creation and manipulation of RDF graphs

• RDFSuite– ICS, Forth, Greece – The Validating RDF Parser (VRP)– The RDF Schema Specific DataBase (RSSDB) – The RDF Query Language (RQL)


Related WorkRelated Work

• CWM (Closed World Machine):– A popular Semantic Web & RDF program, written in

Python by Tim Berners-Lee and Dan Connolly. – It can handle the Notation3 format, as well as XML

RDF and NTriples, and can perform a number of functions, including applying rules as a forward chaining inference engine.


Semantic Community PortalSemantic Community Portal

Recap: The Recap: The Big Picture of Big Picture of

SWSW


Future WorkFuture Work

• RDF schema-specific validator• Frame-based RDF schema-specific query

language• User interface• Automatic generation of community portals

– Application of digital library and archives

• Automatic generation of FAQs• Agent-Mediated B2B Electronic Commerce• Trust on the web


SummarySummary

• RDF repository– RDF parser and generator using Prolog– RDF triples storage in Prolog and RDB tables– Application program interfaces – User interfaces (inference engine)

• Building community portals• Agent-based architecture• Trust on the Web