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RE: XLink - anyone using?

• To: Nadia.Swaby@p..., xml-dev@l...
• Subject: RE: XLink - anyone using?
• From: "Bullard, Claude L (Len)" <len.bullard@i...>
• Date: Fri, 14 Jan 2005 12:12:34 -0600

A quick link primer:

1.  Links as URIs identify a location of a resource (usually a file with 
data of some type, can be a location within a file of some type, etc). These

are untyped links, meaning, they don't declare a relationship.

2.  Typed links name a relationship.   A bibliographic reference is a 
typed link.  An inverted index is a typed link.

3.  Links may have directionality regardless of the mechanical
implementation 
of the link.   Some links point in one direction (an HTML hyperlink).  Some 
go in two directions (say, Next/Back).

4.  Links may have multiple targets.  The index at the back of the book 
(word plus every location word is used) is an example.  Is that multiple 
links or one link with multiple targets?  That's an implementation detail.

5.  A link may only name a relationship or it may be the control for 
navigating among instances.   The major confusion in linking concepts 
is this aspect.

XLinks go beyond identification or the resource and enable typed links. 
Given that a link for the web is the URI, the rest of that information 
is annotative, that is, a link processor of some kind might use it. 
For example, you often want the links in the bibliography, the links 
in the table of contents, and the links in the index at the back of 
a book to be displayed differently, and certainly, to behave differently.
A click on a table of contents should take you to the location of that 
resource.  A click on the inverted index might display all, none or 
one of the resources.

So linking as a concept seems simple, but it has overtones of identity, 
display and control over navigation.   Not everyone agrees or can agree 
on how that fits into a single set of concepts or implementations.  Also, 
most anything one can do with a multiway link, one can do with multiple 
simple links given some control to display it in.  The classic example 
is a popup menu.

So XLink is neat conceptually, but in practical use, there are easy ways 
to do the same thing without using XLinks.  Without a compelling use case 
shared by a near universal set in the user community, it gets very little 
play outside implementations of link data bases (and again, you should 
look at the inverted index and compare that to systems that implement 
topic maps).

len

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