Further work on Xlink

Didier PH Martin martind at netfolder.com
Tue Jan 25 15:49:28 GMT 2000


Continuing my work on xlinks I discovered that xlink:extended elements do
not fit well with hierarchical structures like required for table of
content. However, simple links are better. Why?

a) What's great about XML is that its structure is hierarchical. So, if a
hierarchical structure is mapped into an XML element hierarchy, we have here
a perfect match since when we read the XML document, the hierarchy is
obvious from its structure.

b) A table of content is usually a hierarchical structure. Each node of the
hierarchy is a topic. Thus, in a table of content a topic may contain an
other topic. The topic containing the others is more abstract and the
contained topics are more particular.

c) In a table of content each node (i.e. topic) is pointing to a location.
Thus, there is a one to one relationship between a topic and a location.
This is why the xlink:simple seems to fit the requirements.

Example of a table of content using xlink:simple elements

<topic xlink:type="simple" xlink:href"#chapter1" xlink:title="chapter1">
	<topic xlink:type="simple" xlink:href="#section1" xlink:title="section1/>
		<topic xlink:type="simple" xlink:href="#paragraph1"
	<topic xlink:type="simple" xlink:href="#section2" xlink:title="section2"/>

an xlink interpreter (it could be implemented in XSLT - by the way, there
where no reactions when I said that an XSLT style sheet can be seen as an
xlink interpreter) can deduce a hierarchical structure for these links and
display them as such, for instance as:


(hope that the indentations will survive the mail agent massage - yes I said
massage not message :-)

Question: why not use the xlink extended to build the TOC hierarchy?
Answer: because the Xlink:extended link contains anchors but itself do not
refer to a resource. An xlink:extended link implies a one to many
relationship. This construct seems more adapted to indexes, where each topic
if found in many locations.

Now a question to the group. I am not so sure after reading the
recommendations if an xlink:simple could be included in an external linkset.
Why would we do that? Let's imagine for a second that we want to encode a
discussion thread about a document. For instance, a specification. Then a
discussion thread is perfectly matched to a hierarchical structure where
each node is having a one to one relationship with a location. Thus, the
usage of the xlink:simple seems more appropriate than the usage of the
xlink:extended in that case. But can we include xlink:simple hierarchies in
external linksets? Or if we do so, is it still called a linkset or did it
became a new kind of things?

Didier PH Martin
Email: martind at netfolder.com
Conferences: Web New York (http://www.mfweb.com)
Book to come soon: XML Pro published by Wrox Press
Products: http://www.netfolder.com

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