Resource Description Framework (RDF)

Presented by:Jonathan Catlett

Presentation Topics Background Overview

Example What is RDF?

History Syntax Conclusion

Background Metadata

Structured data about data Used by clients (web browsers) to

improve discovery and access of distributed information.

Usually imbedded into HTML to tell the browser what information is contained in the page.

Background Ontology

Describes the structure of information at different levels of abstraction.

A tree-like structure which can be used to describe semantics.

Parse trees For this presentation we will use an

ontology only to describe the hierarchy of the resources or information.

OntologyWord

Noun Verb

Cause_to_change_location

Throw, Roll, etc.

Dog, Cat, etc.

Overview The Resource Description

Framework is an infrastructure that enables the exchange of metadata structured in an ontology. Let us show this using an example!

Example! Lets say there is a document

server and a client that would like a list of the documents. Very simple example. We will see sample syntax later.

Client Server

HTTP/ XML metadata

Get document Information

Another Example! What about a server that maintains

bookmarks instead of documents? Pretty simple!

Now what if one of the bookmarks is a link to a script that will list all of the client’s current email on the server? Then the structure gets more complex and

dynamic. This is where the RDF’s ability to handle the

ontology is needed.

What is RDF? Developed by the World Wide Web

Consortium (W3C) to provide a standard for defining an architecture for supporting the vast amount of web metadata.

Implemented using XML! Since it is an application of XML, it

inherits the syntax from XML. Namespaces for example.

What is RDF? Human and machine readable

Machine-readable just means that it maintains the structure of the ontology.

This is very important.

What is RDF? For example, the following two

sentences mean the same thing to a human, but are very different to a machine.

“The author of Document 1 is John Smith” “John Smith is the author of Document 1”

RDF maintains the semantics and is unambiguous.

What is the RDF Data Model?

This is how the data is represented using XML. A Resource is any object identifiable

by a URI. The properties associated with a

resource are property-types. Each property-type has a value. A collection of property-types for the

same resource is called a Description.

RDF Data Model Diagram

Resource1 Resource2Property_type 1 Property_Type 2 "Value"

"Value""Value"

Property_type 3 Property_type 4

What is the RDF Data Model?

These Descriptions are kept unambiguous using the XML syntax and namespaces.

Property-types may also contain collections of values Bags – Simple collection Sequence – Order matters Alternative – If-then type structure.

History How did this all come about you may

ask. Metadata began in 1995 with PICS. Platform for Internet Content Selection

(PICS) Mechanism for communicating ratings of web

pages from server to clients. Content control Introduced a general mechanism for creating

rating system. No fixed set of criteria.

History W3C started thinking about the

general problem of Interned resource description based on the PICS architecture.

W3C formed the PICS-NG (Next Generation) working group.

This eventually led to the development of the Resource Description Framework (RDF)

Syntax Simple document report<? xml version="1.0" ?><RDF xmlns = "http://w3.org/TR/1999/PR-rdf-syntax-19990105#"

xmlns:DC = "http://purl.org/DC#" > 

<Description about = "http://dstc.com.au/report.html" > <DC:Title> The Future of Metadata </DC:Title> <DC:Creator> Jacky Crystal </DC:Creator> <DC:Date> 1998-01-01 </DC:Date> <DC:Subject> Metadata, RDF, Dublin Core </DC:Subject>

</Description></RDF>

Syntax Complex Value...<DC:Creator parseType="Resource">

<vCard:FN> Dr Jacky J Crystal </vCard:FN> <vCard:TITLE> Director </vCard:TITLE> <vCard:EMAIL> jacky@dstc.com.au </vCard:EMAIL> <vCard:ROLE> Researcher </vCard:ROLE>

</DC:Creator>...

Syntax Bag...<DC:Creator>

<Bag> <li> Maddie Azzurii </li> <li> Corky Brown </li> <li> Jacky Crystal </li>

</Bag></DC:Creator>...

Syntax Sequence...<DC:Creator>

<Seq> <li> Maddie Azzurii </li> <li> Corky Brown </li> <li> Jacky Crystal </li>

</Seq></DC:Creator>...

Syntax Alternative...<vCard:ROLE>

<Alt> <li xml:lang="en"> Programmer </li> <li xml:lang="fr"> Programmeur </li> <li xml:lang="it"> Programmatore </li>

</Alt></vCard:ROLE>...

Syntax RDF Schema<? xml version="1.0" ?><RDF xmlns = "http://w3.org/TR/PR-rdf-syntax#" xmlns:RDFS = "http://w3.org/TR/WD-rdf-schema#" > 

<Description ID = "Title" > <type resource = "http://w3.org/TR/PR-rdf-syntax#Property" /> <RDFS:label> Title </RDFS:label> <RDFS:comment> The name given to the resource, usually by the Creator or Publisher

</RDFS:comment></Description> 

<Description ID = "Creator" > <type resource = "http://w3.org/TR/PR-rdf-syntax#Property" /> <RDFS:label> Author or Creator </RDFS:label> <RDFS:comment> The person or organisation primarily responsible for the intellectual

content of the resource </RDFS:comment>

</Description> </RDF>

Conclusion RDF provides a needed standard for

describing resources between client and server.

The next step is to get organizations to use the RDF instead of proprietary resource descriptions.

The increasing popularity of XML and JAVA should help the acceptance of RDF.

Resources An Introduction to the Resource

Description Framework www.dlib.org/dlib/may98/miller/05miller.html

An Idiot’s Guide to the Resource Description Framework

www.dstc.edu.au/Research/Projects/rdf/RDF-Idiot.html

RDF: In Fifty Words or Less www.mozilla.org/rdf/50-words.html