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RE: multidirectional links with XLINK

• From: "DuCharme, Robert" <DuCharmR@m...>
• To: "'Friedhelm Krebs'" <krebs@u...>, xml-dev@i...
• Date: Tue, 21 Sep 1999 13:06:40 -0400

>Reading the X-Link-Specification I found the keyword
>multidirectional-link, but I had no idea how to realize it with X-Link.
>What´s the difference to, for instance, two uni-directional links, one
>on each side?

(I'll give it a shot; all corrections welcome.)

XLink lets you declare linking elements that have the job of defining links
(that is, identifying relationships) between resources. Let's say I declare
an element type called myLink that I'll use to link pairs of web pages
having a certain relationship. Once a given myLink element defines a
relationship between http://foo.com/a.html and http://bar.com/b.html, that
link may be implemented in such a way that someone at either end of the link
can travel to the other link, unless I used XLink's arc feature to restrict
such travel in myLink links. With no use of the arc feature, it's one single
myLink linking element defining a multidirectional link.

Because you can't do this in HTML, you would implement the same idea with
two <A HREF="..." NAME="...">, one in http://foo.com/a.html and one in
http://bar.com/b.html, and each pointing at the other. It may look the same
to the end user following the links, but two uni-directional A elements were
necessary to code it instead of a single myLink element.

By "realize," I guess you mean "implement."  Just as the XML spec tells how
you might define an EMPHASIS element type but doesn't tell you how to
implement your emphasis (e.g. when converting to HTML, you might use Perl to
convert an EMPHASIS element to a B element), XLink doesn't tell you about
implementation either. (Well, it drops hints here and there, and I look
forward to implementers picking up on these hints, but they're waiting for
it to reach Recommendation status.) Instead, it tells you how to define and
encode relationships.

For now, the implementation of such a myLink link element could mean writing
out as many <A HREF="..." NAME="..."> elements as are necessary, if you have
write access to the linked resources, or reading the pages in and inserting
the links in a copy or...whatever. Like I said, I look forward to
implementations that let us really have fun with these cool XLink features.

Bob DuCharme       www.snee.com/bob       <bob@  
snee.com>  see www.snee.com/bob/xmlann for "XML:
The Annotated Specification" from Prentice Hall.

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