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| </style><title>Namespaces</title></head><body bgcolor="#8b7765" text="#000000" link="#000000" 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="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">News</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="guidelines.html">XML Guidelines</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://garypennington.net/libxml2/">Solaris binaries</a></li><li><a href="http://www.zveno.com/open_source/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal 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 by |
| recognizing namespace constructs in the input, and does namespace lookup |
| automatically when building the DOM tree. A namespace declaration is |
| associated with an in-memory structure and all elements or attributes within |
| that namespace point to it. Hence testing the namespace is a simple and fast |
| equality operation at the user level.</p><p>I suggest that people using libxml2 use a namespace, and declare it in the |
| root element of their document as the default namespace. Then they don't need |
| to use the prefix in the content but we will have a basis for future semantic |
| refinement and merging of data from different sources. This doesn't increase |
| the size of the XML output significantly, but significantly increases its |
| value 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 have to |
| point to any existing resource on the Web. It will bind all the element and |
| attributes with that URL. I suggest to use an URL within a domain you |
| control, and that the URL should contain some kind of version information if |
| possible. For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a |
| good namespace scheme.</p><p>Then when you load a file, make sure that a namespace carrying the |
| version-independent prefix is installed on the root element of your document, |
| and if the version information don't match something you know, warn the user |
| and be liberal in what you accept as the input. Also do *not* try to base |
| namespace checking on the prefix value. <foo:text> may be exactly the |
| same as <bar:text> in another document. What really matters is the URI |
| associated with the element or the attribute, not the prefix string (which is |
| just a shortcut for the full URI). In libxml, element and attributes have an |
| <code>ns</code> field pointing to an xmlNs structure detailing the namespace |
| prefix and its URI.</p><p>@@Interfaces@@</p><p>@@Examples@@</p><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 strongly |
| suggest adding namespaces to your document. A default namespace scheme |
| <code>xmlns="http://...."</code> should not break validity even on less |
| flexible parsers. Using namespaces to mix and differentiate content coming |
| from multiple DTDs will certainly break current validation schemes. I will |
| try to provide ways to do this, but this may not be portable or |
| standardized.</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> |