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XML and RDF

Paul Miller

Interoperability FocusUK Office for Library & Information Networking (UKOLN)

P.Miller@ukoln.ac.uk http://www.ukoln.ac.uk/

UKOLN is funded by Resource: the Council for Museums, Archives and Libraries, the Joint Information Systems Committee (JISC) of the Further and Higher Education Funding Councils, as well as by project funding from JISC and the EU. UKOLN also receives support from the Universities of Bath and Hull where staff are based.

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What is HTML ?

• HyperText Markup Language• World Wide Web Consortium

recommendation (currently at version 4.01)• Simplified subset of SGML for use on Web• Widely deployed and understood• Difficult to extend• Supported by major vendors, mostly• Technically superseded by XHTML now….

See www.w3.org/MarkUp/See www.w3.org/MarkUp/

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HTML Features

• Easy to create• MS Word, etc.

• Permissive<p><UL><li>Blah…</p>

</ul>

• Occasionally ambiguous

• Case Insensitive.

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What is XML ?

• eXtensible Markup Language• World Wide Web Consortium

recommendation• Simplified subset of SGML for use on Web• Addresses HTML’s lack of evolvability• Easily extended• Supported by major vendors• Increasingly used as a transfer syntax, but

capable of far more….

See www.w3.org/XML/See www.w3.org/XML/

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XML Features

• Extensible• Stricter than HTML on some rules

• Therefore less ambiguous

• Case Sensitive• Notions of ‘well–formed’ and ‘valid’

• A well formed document obeys the rules of XML

• A valid document further obeys the constraints of an associated DTD or equivalent.

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What is XHTML ?

• XHTML 1.0• An expression of HTML 4.01 in XML• The current W3C recommendation for

creating web documents

• XHTML 1.1• A strict expression of HTML 4.01 in

XML– Layout tagging removed altogether– Constructed in a modular fashion

• Currently a W3C proposal.

See www.w3.org/MarkUp/See www.w3.org/MarkUp/

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XHTML Features

…which apply to other applications of XML, such as RDF…

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XHTML Features

• Tags and values are case sensitive<P>Blah… </P>

<P>Blah… </p>

<p>Blah… </p>

• All different. Only one is correct.

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XHTML Features

• All tags must nest<p>here is a paragraph containing <em>emphasis.</p></em>

<p>here is a paragraph containing <em>emphasis.</em></p>

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XHTML Features

• All tags must close<p>here is a paragraph.

<p>here is a paragraph.</p>

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XHTML Features

• Attribute values must be quoted<img src=image.gif alt=Some explanatory text>

<img src=“image.gif” alt=“Some explanatory text” />

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XHTML Features

• Empty elements must close, too<br>

<br></br>

<br />

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Beyond XML

“…XML allows users to add arbitrary structure to their documents but says nothing about what the structures mean.”

See http://www.sciam.com/2001/0501issue/0501berners-lee.html

See http://www.sciam.com/2001/0501issue/0501berners-lee.html

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• World Wide Web Consortium Recommendation

• Fully compliant application of XML• Improves upon XML, HTML, PICS…• Machine understandable metadata!• Supports structure• Increasing interest.

See www.w3.org/RDF/See www.w3.org/RDF/

What is RDF?

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What is RDF?

• Founded upon ‘triples’• A resource has properties• Each property has a value

• e.g.• This presentation has a creator• The creator is “Paul Miller” • This presentation has a title• The title is “XML and RDF”.

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RDF model

ResourceProperty

ValueResource

Statement

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RDF model

ResourceCreator

“Paul Miller”