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XLink question re: arc duplication

• To: "XML Dev" <xml-dev@l...>
• Subject: XLink question re: arc duplication
• From: "Adam van den Hoven" <list@a...>
• Date: Tue, 8 Oct 2002 17:31:05 -0700
• Importance: Normal
• Organization: CUCBC
• Reply-to: <list@a...>

Can someone explain to me the reasoning behind
http://www.w3.org/TR/xlink/#cn-arc-duplicates?

It seems to me that it would be more useful to make the constraint that
to, from and arcrole are unique, not just from and to. I'm not sure why
two resources could not be related in two different ways. For example,
consider the following which might represent a class (modified from the
rec): 

<extendedlink xlink:type="extended">
  <loc xlink:type="locator" xlink:href="..." xlink:label="parent1"
xlink:title="p1" />
  <loc xlink:type="locator" xlink:href="..." xlink:label="parent2"
xlink:title="p2" />
  <loc xlink:type="locator" xlink:href="..." xlink:label="parent3"
xlink:title="p3" />
  <loc xlink:type="locator" xlink:href="..." xlink:label="child1"
xlink:title="c1" />
  <loc xlink:type="locator" xlink:href="..." xlink:label="child2"
xlink:title="c2" />
  <loc xlink:type="locator" xlink:href="..." xlink:label="child3"
xlink:title="c3" />  
  <go xlink:type="arc" xlink:from="parent1" xlink:to="child1"
xlink:arcrole=".../teacher"/>
  <go xlink:type="arc" xlink:from="parent1" xlink:to="child2"
xlink:arcrole=".../teacher"/>
  <go xlink:type="arc" xlink:from="parent1" xlink:to="child3"
xlink:arcrole=".../teacher"/>
  <go xlink:type="arc" xlink:from="parent1" xlink:to="child1"
xlink:arcrole=".../mother"/>
  <go xlink:type="arc" xlink:from="parent2" xlink:to="child2"
xlink:arcrole=".../father"/>
  <go xlink:type="arc" xlink:from="parent3" xlink:to="child3"
xlink:arcrole=".../mother"/>
</extendedlink>

Now this fails the arc constraint but I would argue that they are
semantically unique. I've come across one situation where this sort of
thing would be very useful (but I'm loath to go it alone... Someone once
told me its better to be standard than right). Now it seems that I'll
have to go through the awkward step of duplicating locators so I can
follow the rec (or I have to redo my semantics). 

I know that many people don't particularly like XLink, but I think it's
a worth while tool for doing these sorts of things.  

H. Adam van den Hoven
Web Developer
Credit Union Central of BC

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