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⟶ CISD and DCI ⟶ Literature ⟶ W3C UK News (1998-2006)
⟶ CISD and DCI ⟶ Literature ⟶ W3C UK News (1998-2006)
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Issue 34: October 2000

XML becomes a Recommendation again!

You will be pleased to know that this is not a new XML language but it is significant in that it factors back into the XML document the 109 Errata that have been accumulating since the original version was issued.

Many New Candidate Recommendations this Month

October proved a very fruitful month with the following moving to Candidate Recommendation status:

XBase

XBase is used by XLink and has similar functionality to the HTML BASE element. Suppose you have in XML:

<root xml:base="http://mycompany.org">
<reference xlink:type="simple" xlink:href="new.xml">what's new</reference>
</root>

The simple link would resolve to http://mycompany.org/new.xml. The base attribute can be nested so that you have URLs depending on more than one base.

XML Schemas

XML Schema comes in three parts:

The Primer is a very good introduction with a good running example throughout the text. The other two parts are fairly heavy going. Essentially an XML Schema provides a replacement for much of an XML DTD but with stronger datatyping. Here is a simple XML document:

<exam course="cs203">
<student>Fred Smith</student>
<qapair>
<question>Who is the last King of England</question>
<answer>George VI</answer>
</qapair>
<qapair>
<question>How many queens were named Elizabeth </question>
<answer>Two</answer>
</qapair>
</exam>

This might have a DTD like:

 <!ELEMENT exam (student , (qapair)*) >
 <!ATTLIST exam course CDATA #REQUIRED>
 <!ELEMENT student (#PCDATA)  >
 <!ELEMENT qapair (question,answer)  >
 <!ELEMENT question (#PCDATA)  >
 <!ELEMENT answer (#PCDATA)  >

If this was expressed in XML Schemas it might look like:

<schema>
  <element name="exam">
  <complexType>
    <sequence>
      <element name="student" type="string" />
      <element name="qapair" minOccurs="0" maxOccurs="unbounded">
      <complexType>
        <sequence>
          <element name="question" type="string" />
          <element name="answer" type="string" />
        </sequence>
      </complexType>
      </element>
    </sequence>
  </complexType>
  </element>
</schema>

The good news is that it is in XML so that everything you can do with XML you can do with XML Schemas. The bad news is that they tend to be a bit more verbose. So far, we have not put any further constraints on the datatypes. But if the Course Names had to be two capital letters followed by three digits, we would need to add:

<schema>
  <element name="exam">
    <complexType>
      <attribute name="paper" type="course" />
      <simpleType name="course" />
      <restriction base="string">
      <pattern value="[A-Z]{2}\d{3}" />
      </restriction>
    </complexType>
  </element>
</schema>

So one of the additional features that we get with XML Schemas is stronger datatyping applied to the attributes. Some of the syntax used in the XML Schemas changed quite late on so you will not see words like "bounded" in earlier versions.

XML Signature and Canonical XML

XML Signature Core Syntax and Processing describes how you would define a digital signature as part of a document or detached from it. The signature is something like:

<Signature> 
  <SignedInfo>
    <CanonicalizationMethod  Algorithm="htpp://..." />
    <SignatureMethod   Algorithm="http://...."  />
    <Reference  URI="http:www.w3.org/MyDocument.html" />
      <Transforms>
         <Transform Algorithm="http://www.w3.org/MyXSLTransform.xsl" />
      </Transforms>
      <DigestMethod Algorithm="http://..." />
      <DigestValue>.....</DigestValue>
    </Reference>
  </SignedInfo>
  <SignatureValue>....</SignatureValue> 
  <KeyInfo>
    <KeyValue>
     - - - -
    </KeyValue>
  </KeyInfo>
</Signature>

The SignedInfo section is the thing that is being signed. The requirement is that performing canonicalisation and the signature method on MyDocument should produce the SignatureValue. KeyInfo indicates the key to be used to validate the signature. The Transforms allow you to perform an XSLT transformation over the document so that the part being signed is a subset of the complete document. So, for example, you can embed the signature in the document yet sign everything other than the signature.

Canonicalization ensures that two documents that are effectively the same will have the same value when the signature method is applied. The Canonical XML Candidate Recommendation defines the canonical form of a document. For example, it specifies the order of attributes in an element, gets rid of white space variations and ensures that null elements are the same irrespective of the way they are written.

WWW10 Papers Due

The Tenth International World Wide Web Conference (WWW10) takes place in Hong Kong, China from May 1-5, 2001.

The deadline for refereed paper submission is 13 November so no time to delay!

Membership of W3C Continues to Rise

The total number of W3C Members has risen to 478 (that is 30 more in the last two months). Recent new Members are:

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