Xlink.html
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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta name="generator" content=
"HTML Tidy for Mac OS X (vers 31 October 2006 - Apple Inc. build 13), see www.w3.org" />
<title>
When to use XLink - Design Issues
</title>
<link rel="Stylesheet" href="di.css" type="text/css" />
<meta http-equiv="Content-Type" content=
"text/html; charset=us-ascii" />
</head>
<body bgcolor="#DDFFDD" text="#000000" lang="en" xml:lang="en">
<address>
Tim Berners-Lee<br />
Created Date: 2002/06, last change: $Date: 2002/07/01
18:33:45 $ Z<br />
Status: personal view only. Editing status: first draft.
</address>
<p>
Written in response to TAG discussion and specifically
<a href="http://www.w3.org/2001/tag/ilist#xlinkScope-23">tag
issue 23</a>
</p>
<p>
<a href="./">Up to Design Issues</a>
</p>
<hr />
<h1>
When should I use XLink?
</h1>
<p>
When we are designing a new XML language, and we refer to
something on the web by URI, should we use <a href=
"">XLink</a>?
</p>
<p>
Three possible answers:
</p>
<ol>
<li>No, you don't have to unless there is some functionality
of xlink which you would like to lever.
</li>
<li>You should use xlink whenever your application is one of
hypertext linking, as xlink functionality such as power to
control user interface behavior on link traversal is useful
and should be implemented in a standard way to allow
interoperability.
</li>
<li>You should always make an XLink whenever you make a
reference with a URI, as all such references are in some way
a link.
</li>
</ol>
<p>
The short answer in my humble opinion, is that (2) is right.
</p>
<p>
When an application uses functionality which is within the
scope of Xlink, it should use xlink. To do otherwise breaks
the principle that we are trying to make an interoperable
web.
</p>
<p>
The third extreme case, that xlink should always be used, is
not tenable, as URIs are used generally as identifiers for
everything. Paul Cotton and David Orchard pointed out on a
TAG call (2002/6/17) that the scope of Xlink is hypertext
linking. A motivation for XLink was to give to languages for
human documents a much richer form of hypertext than HTML,
with features which had in fact been used in hypertext
products for many years before the web.
</p>
<p>
A counter-example is the speech grammar specification, which
uses a URI parameter to refer to a piece of grammar in an
external file. This logical information is not intended to be
browsed by people as a document. There is no need for the
hypertext functionality of Xlink. There is no need to clutter
the language with xlink:href syntax.
</p>
<p>
The idea that all uses of URIs are formally hypertext links
does not use the term <em>hypertext</em> in the sense I use
here, or in the sense in which hypertext link functionality
is the scope of Xlink.
</p>
<p>
The XHTML specification does not use xlink, as (I understand)
the working group felt that it was too clumsy to use a
different namespace, and they wanted it to look like HTML,
which uses href=. The group is (2002/06) looking at schema
annotation ways of declaring html:href to carry the
significance of an xlink. These are known as "hlink". The
pros and cons of schema annotation in general as a means to
add semantics or style to a langauge are currently under
debate in the community.
</p>
<hr />
<p>
<a href="Overview.html">Up to Design Issues</a>
</p>
<p>
<a href="../People/Berners-Lee">Tim BL</a>
</p>
</body>
</html>