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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 & 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>supportbyrecognizing namespace constructs in the input, and
does namespacelookupautomatically when building the DOM tree. A namespace
declarationisassociated with an in-memory structure and all elements or
attributeswithinthat namespace point to it. Hence testing the namespace is a
simple andfastequality operation at the user level.</p><p>I suggest that people using libxml2 use a namespace, and declare it
intheroot element of their document as the default namespace. Then they
don'tneedto use the prefix in the content but we will have a basis for
futuresemanticrefinement and merging of data from different sources. This
doesn'tincreasethe size of the XML output significantly, but significantly
increasesitsvalue in the long-term. Example:</p><pre><mydoc xmlns="http://mydoc.example.org/schemas/">
<elem1>...</elem1>
<elem2>...</elem2>
</mydoc></pre><p>The namespace value has to be an absolute URL, but the URL doesn't
havetopoint to any existing resource on the Web. It will bind all the
elementandattributes with that URL. I suggest to use an URL within a
domainyoucontrol, and that the URL should contain some kind of version
informationifpossible. For example,
<code>"http://www.gnome.org/gnumeric/1.0/"</code>isagood namespace scheme.</p><p>Then when you load a file, make sure that a namespace
carryingtheversion-independent prefix is installed on the root element of
yourdocument,and if the version information don't match something you know,
warnthe userand be liberal in what you accept as the input. Also do *not* try
tobasenamespace checking on the prefix value. <foo:text> may be
exactlythesame as <bar:text> in another document. What really matters
is theURIassociated with the element or the attribute, not the prefix string
(whichisjust a shortcut for the full URI). In libxml, element and attributes
havean<code>ns</code>field pointing to an xmlNs structure detailing
thenamespaceprefix and its URI.</p><p>@@Interfaces@@</p><pre>xmlNodePtr node;
if(!strncmp(node->name,"mytag",5)
&& node->ns
&& !strcmp(node->ns->href,"http://www.mysite.com/myns/1.0")) {
...
}</pre><p>Usually people object to using namespaces together with validitychecking.I
will try to make sure that using namespaces won't break validitychecking,so
even if you plan to use or currently are using validation Istronglysuggest
adding namespaces to your document. A default
namespacescheme<code>xmlns="http://...."</code>should not break validity even
onlessflexible parsers. Using namespaces to mix and differentiate
contentcomingfrom multiple DTDs will certainly break current validation
schemes. Tochecksuch documents one needs to use schema-validation, which is
supportedinlibxml2 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>
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