[xtm-wg] XTM-ISS Important XLink difference in DTDs

[Philip Rutherford <philipr@weborganic.com>]

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It seems to me that there is an important XLink difference between
STEP's DTD (tm.dtd) and Michel Biezunski's DTD (mb.dtd). In STEP's DTD
the <topic> element is the extended XLink and it contains <occurs>
elements which are the XLink locators. In Michel's DTD however it is the
<occurs> element that would be the extended XLink, and it contains
<locator> elements which are then the XLink locators.

For my own application of XTMs which is in describing web site structure
I prefer Michel's DTD because it gives greater ability to add resource
meta data to each <occurs> element. The example below uses Michel's DTD
to describe a simple web site containing two documents: welcome.html and
contact.html. This DTD allows separate descriptions of the two documents
to be added using the XLink resource type element, as can be seen below.

    <topicmap>
         <topic id="http://mycompany.com">
             <topname>
                 <basename>My Company's Home Page</basename>
             </topname>
             <occurs xlink:type="extended">
                 <locator xlink:type="locator"
xlink:href="http://mycompany.com" />
                 <locator xlink:type="locator"
xlink:href="http://mycompany.com/welcome.html" />
                 <my:resouce xlink:type="resource"
xlink:role="description">
                         This is a welcome message from the managing
director.
                 </my:resource>
             </occurs>
             <occurs xlink:type="extended">
                 <locator xlink:type="locator"
xlink:href="http://mycompany.com" />
                 <locator xlink:type="locator"
xlink:href="http://mycompany.com/contact.html" />
                 <my:resouce xlink:type="resource"
xlink:role="description">
                         A list of phone numbers, post and email
addresses for the company.
                 </my:resource>
             </occurs>
         </topic>
     </topicmap>

Below is the same example using STEP's DTD. Without adding the
complexity of <arc> elements there is no way of defining which resource
description goes with which locator and thus this information would be
lost in the interchange.

    <topicmap>
         <topic xlink:type="extended" id="http://mycompany.com">
             <topname>
                 <basename>My Company's Home Page</basename>
             </topname>
             <occurs xlink:type="locator"
xlink:href="http://mycompany.com/welcome.html" />
             <occurs xlink:type="locator"
xlink:href="http://mycompany.com/contact.html" />
             <my:resouce xlink:type="resource" xlink:role="description">

                     This is a welcome message from the managing
director.
             </my:resource>
             <my:resouce xlink:type="resource" xlink:role="description">

                     A list of phone numbers, post and email addresses
for the company.
             </my:resource>
             </occurs>
         </topic>
     </topicmap>

Even though Michel's DTD may add an extra element to the ISO standard I
think it makes the definition more powerful when used in conjunction
with XLink especially where a topic has many occurrences. It also gives
occurrences the same XLink status as associations which seems to make
more sense in terms of symmetry and may also make it easier to implement
in practical situations.

What are other peoples feelings on this?

Regards
--Philip

--------------------------------------------------------------
Philip Rutherford               E-mail: philipr@weborganic.com
Weborganic Systems Pty. Ltd.         http://www.weborganic.com
"working together on the web"
Level 10, 91 York St, Sydney 2000, Australia.
Tel: +61 2 9262 4777
Fax: +61 2 9262 4774



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