Resource Description Framework (RDF)

1
Resource Description Framework (RDF)

• Presented by
• Jonathan Catlett

2
Presentation Topics

• Background
• Overview
• Example
• What is RDF?
• History
• Syntax
• Conclusion

3
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.

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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.

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Ontology
6
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!

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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.

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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 clients current
  email on the server?
• Then the structure gets more complex and dynamic.
• This is where the RDFs ability to handle the
  ontology is needed.

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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.

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What is RDF?

• Human and machine readable
• Machine-readable just means that it maintains the
  structure of the ontology.
• This is very important.

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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.

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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.

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RDF Data Model Diagram
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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.

15
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.

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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)

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Syntax

• Simple document report
• lt? xml version"1.0" ?gt
• ltRDF xmlns "http//w3.org/TR/1999/PR-rdf-syntax-
  19990105"
• xmlnsDC "http//purl.org/DC" gt 
• ltDescription about "http//dstc.com.au/report.h
  tml" gt
• ltDCTitlegt The Future of Metadata lt/DCTitlegt
  
• ltDCCreatorgt Jacky Crystal lt/DCCreatorgt
• ltDCDategt 1998-01-01 lt/DCDategt
• ltDCSubjectgt Metadata, RDF, Dublin Core
  lt/DCSubjectgt
• lt/Descriptiongt
• lt/RDFgt

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Syntax

• Complex Value
• ...
• ltDCCreator parseType"Resource"gt
• ltvCardFNgt Dr Jacky J Crystal lt/vCardFNgt
• ltvCardTITLEgt Director lt/vCardTITLEgt
• ltvCardEMAILgt jacky_at_dstc.com.au lt/vCardEMAILgt
  
• ltvCardROLEgt Researcher lt/vCardROLEgt
• lt/DCCreatorgt
• ...

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Syntax

• Bag
• ...
• ltDCCreatorgt
• ltBaggt
• ltligt Maddie Azzurii lt/ligt
• ltligt Corky Brown lt/ligt
• ltligt Jacky Crystal lt/ligt
• lt/Baggt
• lt/DCCreatorgt
• ...

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Syntax

• Sequence
• ...
• ltDCCreatorgt
• ltSeqgt
• ltligt Maddie Azzurii lt/ligt
• ltligt Corky Brown lt/ligt
• ltligt Jacky Crystal lt/ligt
• lt/Seqgt
• lt/DCCreatorgt
• ...

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Syntax

• Alternative
• ...
• ltvCardROLEgt
• ltAltgt
• ltli xmllang"en"gt Programmer lt/ligt
• ltli xmllang"fr"gt Programmeur lt/ligt
• ltli xmllang"it"gt Programmatore lt/ligt
• lt/Altgt
• lt/vCardROLEgt
• ...

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Syntax

• RDF Schema
• lt? xml version"1.0" ?gt
• ltRDF xmlns "http//w3.org/TR/PR-rdf-syntax"
  xmlnsRDFS "http//w3.org/TR/WD-rdf-schema"
  gt 
• ltDescription ID "Title" gt
• lttype resource "http//w3.org/TR/PR-rdf-syntax
  Property" /gt
• ltRDFSlabelgt Title lt/RDFSlabelgt
• ltRDFScommentgt The name given to the resource,
  usually by the Creator or Publisher
  lt/RDFScommentgt
• lt/Descriptiongt 
• ltDescription ID "Creator" gt
• lttype resource "http//w3.org/TR/PR-rdf-syntax
  Property" /gt
• ltRDFSlabelgt Author or Creator lt/RDFSlabelgt
  
• ltRDFScommentgt The person or organisation
  primarily responsible for the intellectual
• content of the resource
• lt/RDFScommentgt
• lt/Descriptiongt 
• lt/RDFgt

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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.

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Resources

• An Introduction to the Resource Description
  Framework
• www.dlib.org/dlib/may98/miller/05miller.html
• An Idiots Guide to the Resource Description
  Framework
• www.dstc.edu.au/Research/Projects/rdf/RDF-Idiot.ht
  ml
• RDF In Fifty Words or Less
• www.mozilla.org/rdf/50-words.html