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XML and RDF
Paul Miller
Interoperability Focus
UK Office for Library & Information Networking (UKOLN)
[email protected]
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
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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• Technically superseded by XHTML now….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/
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© Cabinet Office, Crown Copyright Reserved
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© Cabinet Office, Crown Copyright Reserved
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/
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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.
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See www.w3.org/MarkUp/
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© CCTA, Crown Copyright Reserved
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© CCTA, Crown Copyright Reserved
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


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<p>here is a paragraph containing
<em>emphasis.</p></em>
<p>here is a paragraph containing
<em>emphasis.</em></p>
XHTML Features


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• All tags must close
<p>here is a paragraph.
<p>here is a paragraph.</p>
XHTML Features
• Attribute values must be quoted

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<img src=image.gif
alt=Some explanatory text>
<img src=“image.gif”
alt=“Some explanatory text” />
XHTML Features



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• Empty elements must close, too
<br>
<br></br>
<br />
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
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What is RDF?
• 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/
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What is RDF?
• Founded upon ‘triples’
• A resource has properties
• Each property has a value
• e.g.
•
•
•
•
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This presentation has a creator
The creator is “Paul Miller”
This presentation has a title
The title is “XML and RDF”.
RDF model
Property
Resource
Value
Resource
Statement
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RDF model
Creator
Resource
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“Paul Miller”