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</style><title>Namespaces</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo" /></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo" /></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo" /></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"><h1>The XML C parser and toolkit of Gnome</h1><h2>Namespaces</h2></td></tr></table></td></tr></table></td></tr></table><table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html">Home</a></li><li><a href="html/index.html">Reference Manual</a></li><li><a href="intro.html">Introduction</a></li><li><a href="FAQ.html">FAQ</a></li><li><a href="docs.html" style="font-weight:bold">Developer Menu</a></li><li><a href="bugs.html">Reporting bugs and getting help</a></li><li><a href="help.html">How to help</a></li><li><a href="downloads.html">Downloads</a></li><li><a href="news.html">Releases</a></li><li><a href="XMLinfo.html">XML</a></li><li><a href="XSLT.html">XSLT</a></li><li><a href="xmldtd.html">Validation &amp; DTDs</a></li><li><a href="encoding.html">Encodings support</a></li><li><a href="catalog.html">Catalog support</a></li><li><a href="namespaces.html">Namespaces</a></li><li><a href="contribs.html">Contributions</a></li><li><a href="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a href="html/index.html" style="font-weight:bold">API Menu</a></li><li><a href="guidelines.html">XML Guidelines</a></li><li><a href="ChangeLog.html">Recent Changes</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li><li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li><li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li><li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li><li><a href="ftp://xmlsoft.org/">FTP</a></li><li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li><li><a href="http://www.blastwave.org/packages.php/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://libxmlplusplus.sourceforge.net/">C++ bindings</a></li><li><a href="http://www.zend.com/php5/articles/php5-xmlphp.php#Heading4">PHP bindings</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li><li><a href="http://libxml.rubyforge.org/">Ruby bindings</a></li><li><a href="http://tclxml.sourceforge.net/">Tcl bindings</a></li><li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>The libxml2 library implements <a href="http://www.w3.org/TR/REC-xml-names/">XML namespaces</a>support
byrecognizing namespace constructs in the input, and does namespace
lookupautomatically when building the DOM tree. A namespace declaration
isassociated with an in-memory structure and all elements or attributes
withinthat namespace point to it. Hence testing the namespace is a simple and
fastequality operation at the user level.</p><p>I suggest that people using libxml2 use a namespace, and declare it in
theroot element of their document as the default namespace. Then they don't
needto use the prefix in the content but we will have a basis for future
semanticrefinement and  merging of data from different sources. This doesn't
increasethe size of the XML output significantly, but significantly increases
itsvalue in the long-term. Example:</p><pre>&lt;mydoc xmlns="http://mydoc.example.org/schemas/"&gt;
   &lt;elem1&gt;...&lt;/elem1&gt;
   &lt;elem2&gt;...&lt;/elem2&gt;
&lt;/mydoc&gt;</pre><p>The namespace value has to be an absolute URL, but the URL doesn't have
topoint to any existing resource on the Web. It will bind all the element
andattributes with that URL. I suggest to use an URL within a domain
youcontrol, and that the URL should contain some kind of version information
ifpossible. For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code>is
agood namespace scheme.</p><p>Then when you load a file, make sure that a namespace carrying
theversion-independent prefix is installed on the root element of your
document,and if the version information don't match something you know, warn
the userand be liberal in what you accept as the input. Also do *not* try to
basenamespace checking on the prefix value. &lt;foo:text&gt; may be exactly
thesame as &lt;bar:text&gt; in another document. What really matters is the
URIassociated with the element or the attribute, not the prefix string (which
isjust a shortcut for the full URI). In libxml, element and attributes have
an<code>ns</code>field pointing to an xmlNs structure detailing the
namespaceprefix and its URI.</p><p>@@Interfaces@@</p><pre>xmlNodePtr node;
if(!strncmp(node-&gt;name,"mytag",5)
  &amp;&amp; node-&gt;ns
  &amp;&amp; !strcmp(node-&gt;ns-&gt;href,"http://www.mysite.com/myns/1.0")) {
  ...
}</pre><p>Usually people object to using namespaces together with validity
checking.I will try to make sure that using namespaces won't break validity
checking,so even if you plan to use or currently are using validation I
stronglysuggest adding namespaces to your document. A default namespace
scheme<code>xmlns="http://...."</code>should not break validity even on
lessflexible parsers. Using namespaces to mix and differentiate content
comingfrom multiple DTDs will certainly break current validation schemes. To
checksuch documents one needs to use schema-validation, which is supported
inlibxml2 as well. See <a href="http://www.relaxng.org/">relagx-ng</a>and <a href="http://www.w3c.org/XML/Schema">w3c-schema</a>.</p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>