RDF: Resource Description Framework

RDF: Resource Description Framework

Jianguo Lu University of Windsor

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Contents

• Ontology• Syntax of RDF and RDFS• Axiomatic Semantics for RDF and RDFS• Applications of RDF and RDFS

– Querying of RDF/RDFS Documents using RQL

3

Web Today

[Hendler & Miller 02]

4

The semantic web

5

Ontology

• Long history coming from Philosophy, introduced by Aristotle

– “a branch of metaphysics concerned with the nature and relations of being” --Webster

• Picked up by the Artificial Intelligence– “For AI systems, what ‘exists’ is that which can be represented”

– “a shared and common understanding of some domain that can be communicated between people and application systems” – Gruber

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What is Ontology

• An ontology is a formal, explicit specification of a shared conceptualization - Gruber– Conceptualization refers to an abstract model of phenomena.– Explicit means that the type of concepts used, and the

constraints on their use are explicitly defined. – Formal refers to the fact that the ontology should be machine

readable. – Shared reflects that ontology should capture consensual

knowledge accepted by the communities.

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Main components of an Ontology

• Classes: concepts of the domain or tasks, which are usually organized in taxonomies– in a university ontology, student and professor are two classes

• Relations: a type of interaction between concepts of the domain– such as: subclass-of, is-a

• Axioms: model sentences that are always true– such as: if the student attends both A and B course, then he or she must be

a second year student

• Instances: to represent specific elements– such as: a student called Peter is the instance of Student class

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Contents• Ontology• Syntax of RDF and RDFS• Semantics• Applications

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RDF is a Web Standard

• RDF Model and Syntax Specification became a W3C (World Wide Web Consortium) Recommendation in February 1999.– It has a long history, considering that XML became W3C

Recommendation in 1998.

• The purpose of RDF (Resource Description Framework) is to give a standard way of specifying data "about" something.

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XML vs. RDF<company>

<treatmentOffered>Physiotherapy</treatmentOffered><companyName>Agilitas Physiotherapy Centre </companyName><staff>

<therapist>Lisa Davenport</therapist><therapist>Steve Matthews</therapist><secretary>Kelly Townsend</secretary>

</staff> … …</company>

• How to answer the query “give me the list of staff members in this company”?

• XML provides semantic information as a by-product of defining the structure of the document

• XML prescribes a tree structure for documents and the different leaves of the tree have a well-defined tag and context the information can be understood with.

• That is, structure and semantics of documents are interwoven– there is no intended meaning associated with the nesting of tags– It is up to each application to interpret the nesting.

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RDF and RDF Schema

Lisa therapistisA

staff

therapist

subClassOf

secretary

subClassOf

How to encode the rule that “a person can not be a secretary and therapist at the same time”?

• RDF

• RDF Schema

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OWL (Web Ontology Language)

Lisa therapistisA

secretaryisA

staff

therapist

subClassOf

secretary

Disjoint (therapist, secretary)

RDF

OWL

RDFS

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Basic Ideas of RDF• David Billington is a lecturer of Discrete Maths

<course name="Discrete Maths"><lecturer>David Billington</lecturer>

</course>

<lecturer name="David Billington"><teaches>Discrete Maths</teaches>

</lecturer>– Opposite nesting, same information!

• Basic building block of rdf: subject-predicate-object triple– It is called a statement;– Sentence about Billington is such a statement;

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:mydomain="http://www.mydomain.org/my-rdf-ns#">

<rdf:Description rdf:about="http://www.cit.gu.edu.au/DiscreteMath"> <mydomain:taughtBy> David Billington </mydomain:taughtBy>

</rdf:Description></rdf:RDF>

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Statements

• Statements assert the properties of resources• A statement is an resource-property-value triple

– Sometimes also called subject, predicate, and value

• Values can be resources or literals – Literals are atomic values (strings)

Subject Objectpredicate

Resource Valueproperty

Equivalent!

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Resource in a statement• We can think of a resource as a “thing” we want to talk

about– E.g. authors, books, publishers, places, people, hotels;– Every resource has a URI, a Universal Resource Identifier;– A URI can be

• a URL (Web address), or • some other kind of unique identifier.

– In the following example, “http://www.cit.gu.edu.au/DiscreteMath” is a resource that we want to talk about.

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:mydomain="http://www.mydomain.org/my-rdf-ns#">

<rdf:Description rdf:about="http://www.cit.gu.edu.au/DiscreteMath"> <mydomain:taughtBy> David Billington

</mydomain:taughtBy></rdf:Description>

</rdf:RDF>

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Properties

• Properties are a special kind of resources• They describe relations between resources

– E.g. “taught by”, “written by”, “age”, “title”, etc.;– Properties are also identified by URIs.

• Advantages of using URIs:– Α global, worldwide, unique naming scheme;– Reduces the homonym problem of distributed data

representation.

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:mydomain="http://www.mydomain.org/my-rdf-ns#"> <rdf:Description rdf:about="http://www.cit.gu.edu.au/DiscreteMath"> <mydomain:taughtBy> David Billington </mydomain:taughtBy> </rdf:Description></rdf:RDF>

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Three Views of a Statement

• A triple• A piece of a graph• A piece of XML code

• Thus an RDF document can be viewed as:– A set of triples;– A graph (semantic net);– An XML document.

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RDF Example

• The statement:http://www.example.org/index.html has a creation-date whose value is August 16, 1999

<?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:exterms="http://www.example.org/terms/"> <rdf:Description rdf:about="http://www.example.org/index.html"> <exterms:creation-date>August 16, 1999</exterms:creation-date>

</rdf:Description> </rdf:RDF>

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Several statements about the same resource

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Its XML representation

• A complete representation<rdf:Description rdf:about="http://www.example.org/index.html">

<exterms:creation-date>August 16, 1999</exterms:creation-date>

</rdf:Description>

<rdf:Description rdf:about="http://www.example.org/index.html"> <dc:language>en</dc:language>

</rdf:Description>

<rdf:Description rdf:about="http://www.example.org/index.html"> <dc:creator rdf:resource="http://www.example.org/staffid/85740"/>

</rdf:Description>

• An abbreviation<rdf:Description rdf:about="http://www.example.org/index.html">

<exterms:creation-date> August 16, 1999 </exterms:creation-date>

<dc:language> en </dc:language>

<dc:creator rdf:resource="http://www.example.org/staffid/85740"/>

</rdf:Description>

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Two different kinds of nodes

• Nodes that are URIrefs are shown as ellipses • Nodes that are literals are shown as boxes

• Using URIref to identify resource and property

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Structured Property Values and Blank Nodes

Problem with this approach: may generate many intermediate URIRefs.

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Blank Node

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Blank node or anonymous resource

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Corresponding RDF/XML

<?xml version="1.0"?> <rdf:RDF xmlns:rdf=“http://www.w3.org/1999/02/22-rdf-syntax-ns#”

xmlns:dc=“http://purl.org/dc/elements/1.1/”xmlns:exterms="http://example.org/stuff/1.0/">

<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"> <dc:title>RDF/XML Syntax Specification (Revised)</dc:title> <exterms:editor rdf:nodeID="abc"/> </rdf:Description>

<rdf:Description rdf:nodeID="abc"> <exterms:fullName>Dave Beckett</exterms:fullName><exterms:homePage rdf:resource="http://purl.org/net/dajobe/"/>

</rdf:Description>

</rdf:RDF>

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Typed literals

• 27 is an integer or a string?

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A Typed Literal for a Web Page's Creation Date

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:exterms="http://www.example.org/terms/">

<rdf:Description rdf:about="http://www.example.org/index.html"> <exterms:creation-date rdf:datatype="&xsd;date">1999-08-16 </exterms:creation-date> </rdf:Description>

</rdf:RDF>

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An Invalid Typed Literal for John Smith's Age

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RDF Containers

• Container is a resource to contain things• RDF defines three types of containers:

– Bag: contains an unordered list of value elements– Seq: contains an ordered list of value elements– Alt: contains a list of alternative values for an element:

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Bag

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Bag (cont.)

<rdf:Description rdf:about="http://example.org/courses/6.001">

<s:students>

<rdf:Bag>

<rdf:li rdf:resource="http://example.org/students/Amy"/>

<rdf:li rdf:resource="http://example.org/students/Mohamed"/>

<rdf:li rdf:resource="http://example.org/students/Johann"/>

<rdf:li rdf:resource="http://example.org/students/Maria"/>

<rdf:li rdf:resource="http://example.org/students/Phuong"/>

</rdf:Bag>

</s:students>

</rdf:Description>

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Alt container

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Alt container (cont.)

<rdf:Description rdf:about="http://example.org/packages/X11">

<s:DistributionSite>

<rdf:Alt>

<rdf:li rdf:resource="ftp://ftp.example.org"/>

<rdf:li rdf:resource="ftp://ftp1.example.org"/>

<rdf:li rdf:resource="ftp://ftp2.example.org"/>

</rdf:Alt>

</s:DistributionSite>

</rdf:Description>

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RDF Collection

• A container only says that certain resources are members

• Id does not say that other members do not exist

<rdf:Description rdf:about="http://example.org/courses/6.001"> <s:students rdf:parseType="Collection"> <rdf:Description rdf:about="http://example.org/students/Amy"/> <rdf:Description rdf:about="http://example.org/students/Mohamed"/> <rdf:Description rdf:about="http://example.org/students/Johann"/> </s:students> </rdf:Description>

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RDF Reification

• In RDF it is possible to make statements about statements– Grigoris believes that David Billington is the creator of

http://www.cit.gu.edu.au/~db

• Such statements can be used to describe belief or trust in other statements

• The solution is to assign a unique identifier to each statement– It can be used to refer to the statement

• Introduce an auxiliary object (e.g. belief1) • relate it to each of the 3 parts of the original statement

through the properties subject, predicate and object• In the preceding example

– subject of belief1 is David Billington

– predicate of belief1 is creator

– object of belief1 is http://www.cit.gu.edu.au/~db

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Reification example

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Reification in XML<?xml version="1.0"?> <!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:dc=“http://purl.org/dc/elements/1.1/” xmlns:exterms=“http://www.example.com/terms/” xml:base="http://www.example.com/2002/04/products">

<rdf:Description rdf:ID="item10245"> <exterms:weight rdf:datatype="&xsd;decimal">2.4</exterms:weight>

</rdf:Description>

<rdf:Statement rdf:about="#triple12345"> <rdf:subject rdf:resource="http://www.example.com/2002/04/products#item10245"/><rdf:predicate rdf:resource="http://www.example.com/terms/weight"/><rdf:object rdf:datatype="&xsd;decimal">2.4</rdf:object> <dc:creator rdf:resource="http://www.example.com/staffid/85740"/>

</rdf:Statement> </rdf:RDF>

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rdf:about vs rdf:ID

• An element rdf:Description has– an rdf:about attribute indicating that the resource has been

“defined” elsewhere– An rdf:ID attribute indicating that the resource is defined

• Formally, there is no such thing as “defining” an object in one place and referring to it elsewhere – Sometimes it is useful (for human readability) to have a defining

location, while other locations state “additional” properties.

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Connecting two resources

<rdf:Description rdf:about="CIT1111">

<uni:courseName>Discrete Mathematics</uni:courseName>

<uni:isTaughtBy rdf:resource="949318"/>

</rdf:Description>

<rdf:Description rdf:about="949318">

<uni:name>David Billington</uni:name>

<uni:title>Associate Professor</uni:title>

</rdf:Description>

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Nested description

<rdf:Description rdf:about="CIT1111"><uni:courseName>Discrete Maths</uni:courseName><uni:isTaughtBy>

<rdf:Description rdf:ID="949318"><uni:name>David Billington</uni:name><uni:title>Associate Professor</uni:title>

</rdf:Description></uni:isTaughtBy>

</rdf:Description> <?xml version="1.0"?><Resource-A> <property-A> <Resource-B> <property-B> <Resource-C> <property-C> Value-C </property-C> </Resource-C> </property-B> </Resource-B> </property-A></Resource-A>

value of property-A

value of property-B

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Introducing some Structure to RDF Documents using the rdf:type Element• What does the following RDF describe? Not very

straightforward. <rdf:Description rdf:ID="CIT1111">

<uni:courseName>Discrete Maths</uni:courseName><uni:isTaughtBy rdf:resource="#949318"/>

</rdf:Description>

• Add type declaration<rdf:Description rdf:ID="CIT1111">

<rdf:type rdf:resource="http://www.mydomain.org/uni-ns#course"/><uni:courseName>Discrete Maths</uni:courseName><uni:isTaughtBy rdf:resource="#949318"/>

</rdf:Description>

• An equivalent, more concise notation<uni:course rdf:ID="CIT1111">

<uni:courseName>Discrete Maths</uni:courseName><uni:isTaughtBy rdf:resource="#949318"/>

</rdf:Description>

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Equivalent Representations<River rdf:ID="Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#" xml:base="http://www.china.org/geography/rivers"> <length>6300 kilometers</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

<River rdf:about="http://www.china.org/geography/rivers#Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#"> <length>6300 kilometers</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

<rdf:Description rdf:about="http://www.china.org/geography/rivers#Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#"> <rdf:type rdf:resource="http://www.geodesy.org/river#River"/> <length>6300 kilometers</length> <startingLocation>western China's Qinghai-Tibet Plateau </startingLocation> <endingLocation>East China Sea</endingLocation></rdf:Description>

Note: In the RDF literature the examplesare typically shown in this form.

From Costello

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Resource URI

= concatenation(xml:base, '#', rdf:ID)

= concatenation(http://www.china.org/geography/rivers, '#', "Yangtze")

= http://www.china.org/geography/rivers#Yangtze

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<?xml version="1.0"?><River id="Yangtze" xmlns="http://www.geodesy.org/river" xmlns:uom="http://www.measurements.org/units-of-measure#"> <length uom:units="kilometers">6300</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

RDF does not allow attributes on the properties (except for special RDFattributes such as rdf:resource). So we need to make the uom:units attributea child element.Your first instinct might be to modify length to have two child elements:

<?xml version="1.0"?><River id="Yangtze" xmlns="http://www.geodesy.org/river" xmlns:uom="http://www.measurements.org/units-of-measure#"> <length> <value>6300</value> <uom:units>kilometers</uom:units> </length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

However, nowthe lengthproperty hasas its value twovalues.RDF allows only binary relationsi.e., a single value for aproperty.

Describe a property that has more than one value

From Costello

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Rdf:value

• length has two values - 6300 and kilometers.• RDF provides a special property, rdf:value, to be used for

specifying the "primary" value.– 6300 is the primary value– kilometers is a value which provides additional information about the

primary value.

length6300

kilometers

From Costello

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Anonymous resource

<?xml version="1.0"?><River rdf:ID="Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#" xmlns:uom="http://www.measurements.org/units-of-measure#"> <length> <rdf:Description> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </rdf:Description> </length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

An anonymousresource

From Costello

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rdf:parseType="Resource"

<?xml version="1.0"?><River rdf:ID="Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#" xmlns:uom="http://www.measurements.org/units-of-measure#"> <length rdf:parseType="Resource"> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

If the value of a property is comprised of several values then one option is to create an anonymous resource, as we saw. RDF provides a shorthand,so that you don't need to create an rdf:Description element, by using rdf:parseType="Resource", as shown here:

From Costello

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Equivalent

<length> <rdf:Description> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </rdf:Description></length>

<length rdf:parseType="Resource"> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units></length>

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Exercise

Modify the following XML document so that it is also a valid RDF document:

<?xml version="1.0"?><River id="Yangtze" xmlns="http://www.geodesy.org/river" xmlns:uom="http://www.measurements.org/units-of-measure#"> <length uom:units="kilometers">6300</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation> <Dam id="ThreeGorges" xmlns="http://www.geodesy.org/dam"> <name>The Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam></River>

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Answer<?xml version="1.0"?><River rdf:ID="Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#" xmlns:uom="http://www.measurements.org/units-of-measure#" xml:base="http://www.china.org/geography/rivers"> <length rdf:parseType="Resource"> <rdf:value>6300</rdf:value> <uom:units>kilometers</uom:units> </length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation> <obstacle> <Dam rdf:ID="ThreeGorges" xmlns="http://www.geodesy.org/dam#"> <name>The Three Gorges Dam</name> <width>1.5 miles</width> <height>610 feet</height> <cost>$30 billion</cost> </Dam> </obstacle></River>

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Exercise 2

<?xml version="1.0"?><Meeting id="XML-Design-Patterns" xmlns="http://www.business.org"> <attendees> <name>John Smith</name> <name>Sally Jones</name> </attendees></Meeting>


rdf:Bag makes it clear that this is an unorderedcollection of names.

<?xml version="1.0"?><Meeting rdf:ID="XML-Design-Pattern" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.business.org#"> <attendees> <rdf:Bag> <name>John Smith</name> <name>Sally Jones</name> </rdf:Bag> </attendees></Meeting>

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Exercise 3


<?xml version="1.0"?><Catalogue xmlns="http://www.publishing.org#" xmlns:dc="http://pur1.org/metadata/dublin-core#"> <Book> <dc:Title>Lateral Thinking</dc:Title> <dc:Creator>Edward de Bono</dc:Creator> <dc:Date>1973</dc:Date> <ISBN>0-06-099325-2</ISBN> <dc:Publisher>Harper & Row</dc:Publisher> </Book> <Book> <dc:Title>Illusions: The Adventures of a Reluctant Messiah</dc:Title> <dc:Creator>Richard Bach</dc:Creator> <dc:Date>1977</dc:Date> <ISBN>0-440-34319-4</ISBN> <dc:Publisher>Dell Publishing Co.</dc:Publisher> </Book> <Book> <dc:Title>The First and Last Freedom</dc:Title> <dc:Creator>J. Krishnamurti</dc:Creator> <dc:Date>1954</dc:Date> <ISBN>0-06-064831-7</ISBN> <dc:Publisher>Harper & Row</dc:Publisher> </Book></Catalogue>

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Modification 1: identifiers are added<?xml version="1.0"?><Catalogue id="BookCatalogue" xmlns="http://www.publishing.org#" xmlns:dc="http://pur1.org/metadata/dublin-core#"> <Book id="_0-06-099325-2"> <dc:Title>Lateral Thinking</dc:Title> <dc:Creator>Edward de Bono</dc:Creator> <dc:Date>1973</dc:Date> <dc:Publisher>Harper & Row</dc:Publisher> </Book> <Book id="_0-440-34319-4"> <dc:Title>Illusions: The Adventures of a Reluctant Messiah</dc:Title> <dc:Creator>Richard Bach</dc:Creator> <dc:Date>1977</dc:Date> <dc:Publisher>Dell Publishing Co.</dc:Publisher> </Book> <Book id="_0-06-064831-7"> <dc:Title>The First and Last Freedom</dc:Title> <dc:Creator>J. Krishnamurti</dc:Creator> <dc:Date>1954</dc:Date> <dc:Publisher>Harper & Row</dc:Publisher> </Book></Catalogue>

Notice that the ISBN elements were deleted and their values used as identifiers.

Why was an underscoreplaced in front of theISBN?Answer: The ID datatypedoes not allow an identifier to begin witha digit. So, we (arbitrarily) decided touse an underscore.

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The RDF document<?xml version="1.0"?><Catalogue rdf:ID="BookCatalogue" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.publishing.org#" xmlns:dc="http://pur1.org/metadata/dublin-core#" xml:base="http://www.bn.com"> <item> <Book rdf:ID="_0-06-099325-2" xml:base="http://www.publishing.org/book"> <dc:Title>Lateral Thinking</dc:Title> <dc:Creator>Edward de Bono</dc:Creator> <dc:Date>1973</dc:Date> <dc:Publisher>Harper & Row</dc:Publisher> </Book> </item> <item> <Book rdf:ID="_0-440-34319-4" xml:base="http://www.publishing.org/book"> <dc:Title>Illusions: The Adventures of a Reluctant Messiah</dc:Title> <dc:Creator>Richard Bach</dc:Creator> <dc:Date>1977</dc:Date> <dc:Publisher>Dell Publishing Co.</dc:Publisher> </Book> </item> ...</Catalogue>

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Exercise 4: Draw the graph representation of the following rdf

<?xml version="1.0"?><River rdf:about="http://www.china.org/geography/rivers#Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#"> <length>6300 kilometers</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

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RDF and relational database

Title Artist Country Company Price Year

Empire Burlesque Bob Dylan USA Columbia 10.90 1985

Hide your heart Bonnie Tyler UK CBS Records 9.90 1988

...

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:cd="http://www.recshop.fake/cd">

<rdf:Description rdf:about="http://www.recshop.fake/cd/Empire Burlesque"> <cd:artist>Bob Dylan</cd:artist> <cd:country>USA</cd:country> <cd:company>Columbia</cd:company> <cd:price>10.90</cd:price> <cd:year>1985 </cd:year> </rdf:Description>

<rdf:Description rdf:about="http://www.recshop.fake/cd/Hide your heart"> <cd:artist>Bonnie Tyler</cd:artist> <cd:country>UK</cd:country> <cd:company>CBS Records</cd:company> <cd:price>9.90</cd:price> <cd:year>1988</cd:year> </rdf:Description> </rdf:RDF>

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Properties as Attributes

• Properties can also be expressed as attributes (instead of elements):

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:cd="http://www.recshop.fake/cd">

<rdf:Description rdf:about="http://www.recshop.fake/cd/Empire Burlesque"

cd:artist="Bob Dylan" cd:country="USA"

cd:company="Columbia" cd:price="10.90"

cd:year="1985" />

</rdf:RDF>

• In the example above, the properties (artist, country, company, price, and year) are expressed as attributes instead of elements.

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A Critical View of RDF

• RDF uses only binary properties– This is a restriction because often we use predicates with more than 2

arguments

– But binary predicates can simulate these

• Example: referee(X,Y,Z) – X is the referee in a chess game between players Y and Z

• We introduce:– a new auxiliary resource chessGame

– the binary predicates ref, player1, and player2

• We can represent referee(X,Y,Z) as:

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RDF Parser

• There is a nice RDF parser at the W3 Web site:– http://www.w3.org/RDF/Validator

• This RDF parser will tell you if your XML is in the proper RDF format.

• Altova semanticworks support RDF, RDFS, and OWL.

http://www.w3.org/RDF/Validator

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<River rdf:about="http://www.china.org/geography/rivers#Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#"> <length>6300 kilometers</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

<River rdf:about="http://www.china.org/geography/rivers#Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#"> <name>Dri Chu - Female Yak River</name> <name>Tongtian He, Travelling-Through-the-Heavens River</name> <name>Jinsha Jiang, River of Golden Sand</name> </River>

<River rdf:about="http://www.china.org/geography/rivers#Yangtze" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://www.geodesy.org/river#"> <length>6300 kilometers</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation> <name>Dri Chu - Female Yak River</name> <name>Tongtian He, Travelling-Through-the-Heavens River</name> <name>Jinsha Jiang, River of Golden Sand</name> </River>

Aggregated Data!

Aggregator tool collectsdata about the Yangtze

A distributed network of data!

http://www.china.org/geography/rivers/yangtze.rdf

http://www.encyclopedia.org/yangtze-alternate-names.rdf

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Anonymous resources can’t be aggregated<?xml version="1.0"?><River xmlns="http://www.geodesy.org/river#"> <name>Yangtze</name> <length>6300 kilometers</length> <startingLocation>western China's Qinghai-Tibet Plateau</startingLocation> <endingLocation>East China Sea</endingLocation></River>

http://www.china.org/geography/rivers/yangtze.rdf

<?xml version="1.0"?><River xmlns="http://www.geodesy.org/river#"> <name>Yangtze</name> <name>Dri Chu - Female Yak River</name> <name>Tongtian He, Travelling-Through-the-Heavens River</name> <name>Jinsha Jiang, River of Golden Sand</name> </River>

http://www.encyclopedia.org/yangtze-alternate-names.rdf

An aggregator tool will not be able to determine if these documents are talking about the same resource.

Aggregate