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</style><link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-WG-NOTE.css"></head><body><div class="head"><p><a href="http://www.w3.org/"><img src="http://www.w3.org/Icons/w3c_home" alt="W3C" height="48" width="72"></a></p>
<h1><a name="title" id="title"></a>Extending XLink 1.0 </h1>
<h2><a name="w3c-doctype" id="w3c-doctype"></a>W3C Working Group Note 27 January 2005</h2><dl><dt>This version:</dt><dd>
<a href="http://www.w3.org/TR/2005/NOTE-xlink10-ext-20050127/">http://www.w3.org/TR/2005/NOTE-xlink10-ext-20050127/</a>
</dd><dt>Latest version:</dt><dd>
<a href="http://www.w3.org/TR/xlink10-ext/">http://www.w3.org/TR/xlink10-ext/</a>
</dd><dt>Editor:</dt><dd>Norman Walsh, Sun Microsystems</dd></dl><p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2005 <a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology">MIT</acronym></a>, <a href="http://www.ercim.org/"><acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply.</p></div><hr><div>
<h2><a name="abstract" id="abstract"></a>Abstract</h2><p>This document describes some useful changes that could be incorporated
into an XLink 1.1 Specification.</p></div><div>
<h2><a name="status" id="status"></a>Status of this Document</h2><p><em>This section describes the status of this document at the time
of its publication. Other documents may supersede this document. A
list of current W3C publications and the latest revision of this
technical report can be found in the
<a href="http://www.w3.org/TR/">W3C technical reports index</a>
at http://www.w3.org/TR/.</em></p><p>This document is a
<a href="http://www.w3.org/2004/02/Process-20040205/tr.html#WGNote">W3C
Working Group Note</a>, made available by the
<a href="http://www.w3.org/XML/Core">W3C XML Core Working Group</a>
as part of the
<a href="http://www.w3.org/XML/Activity">XML Activity</a>.
The authors of this document are the XML Core Working
Group participants.</p><p>This WG Note is being published for information purposes only.
The Working Group does not plan to issue updates and therefore
has no current plans or process by which to handle feedback.</p><p>Publication as a Working Group Note does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or
obsoleted by other documents at any time. It is inappropriate to cite this
document as other than work in progress.</p></div><div class="toc">
<h2><a name="contents" id="contents"></a>Table of Contents</h2><p class="toc">1 <a href="#intro">Introduction</a><br>
1.1 <a href="#changes">Proposed Changes</a><br>
</p>
<h3><a name="appendices" id="appendices"></a>Appendix</h3><p class="toc">A <a href="#references">References</a><br>
</p></div><hr><div class="body"><div class="div1">
<h2><a name="intro" id="intro"></a>1 Introduction</h2><p>Since its introduction as a Recommendation,
<a href="#xlink">[XLink]</a> has been adopted
by several markup vocabularies. However, the current trend to migrate
from DTD-based validation to schema-based validation poses additional
challenges that could hamper its continued adoption.</p><p>A few small changes could:</p><ul><li><p>Make XLink easier to use.</p></li><li><p>Reduce its dependence on annotations provided by external grammars
(XML DTDs or XML Schema, for example)</p></li><li><p>Increase interoperability by reducing the risk of markup errors or
misinterpretations.</p></li></ul><div class="div2">
<h3><a name="changes" id="changes"></a>1.1 Proposed Changes</h3><ol class="enumar"><li><p><em>Make simple XLinks an application-level default.</em></p><p>In XLink 1.0, all simple links must be identified explicitly with
an <code>xlink:type</code> attribute. When XLink 1.0 was developed, it
seemed reasonable to depend on DTD validation to provide this default
value when it was a burden to authors to enter it by hand. As XML use
has spread and new validation technologies have been developed, this
is no longer the case.</p><p>Rather than relying on an annotation to provide the simple link
type, it seems prudent to make this an application-level default. In
other words, any element with an <code>xlink:href</code> attribute that
does not specify a link type should be treated as a simple link.</p></li><li><p><em>Reserve all attributes in the XLink namespace.</em></p><p>The current XLink 1.0 Recommendation defines several attributes
in the XLink namespace. It seems prudent to explicitly reserve all
other such attributes for future use. By a strict interpretation of
the current specification, authors and other end-users have free
latitude to use new attributes in the XLink namespace and this was
never intended. Such use would create interoperability problems and
should be prohibited.</p></li><li><p><em>Allow IRIs.</em></p><p>The current specification requires that URIs be used to identify
some XLink properties, such as role and arc types. In the interest of
forward compatibility, these requirements should be amended so that
IRIs are also allowed.</p></li><li><p><em>Provide Sample XML Schema and RELAX NG Grammars.</em></p><p>The current specification provides a non-normative sample DTD.
Given that XML Schema
and RELAX NG are now widely deployed, it makes sense to provide equivalent,
non-normative XML Schema and RELAX NG Grammars.</p></li></ol><p>XLink is not without its critics and it's clearly the case that
these changes do not address all of the criticisms that have been
leveled at XLink. But these changes would make XLink more useful in
the places where it is <em>already</em> being used and would
make XLink practical in a variety of similar vocabularies.</p></div></div></div><div class="back"><div class="div1">
<h2><a name="references" id="references"></a>A References</h2><dl><dt class="label"><a name="xlink" id="xlink"></a>XLink</dt><dd><a href="http://www.w3.org/TR/xlink/"><cite>XML
Linking Language (XLink) Version 1.0</cite></a>. DeRose, Steve, Eve Maler,
and David Orchard, editors. World Wide Web Consortium, 2001. (See http://www.w3.org/TR/xlink/.)</dd></dl></div></div></body></html>