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| 10 | </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://opencsw.org/packages/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://lxml.de/">lxml Python bindings</a></li><li><a href="http://cpan.uwinnipeg.ca/dist/XML-LibXML">Perl bindings</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 by
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| 11 | recognizing namespace constructs in the input, and does namespace lookup
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| 12 | automatically when building the DOM tree. A namespace declaration is
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| 13 | associated with an in-memory structure and all elements or attributes within
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| 14 | that namespace point to it. Hence testing the namespace is a simple and fast
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| 15 | equality operation at the user level.</p><p>I suggest that people using libxml2 use a namespace, and declare it in the
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| 16 | root element of their document as the default namespace. Then they don't need
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| 17 | to use the prefix in the content but we will have a basis for future semantic
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| 18 | refinement and merging of data from different sources. This doesn't increase
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| 19 | the size of the XML output significantly, but significantly increases its
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| 20 | value in the long-term. Example:</p><pre><mydoc xmlns="http://mydoc.example.org/schemas/">
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| 21 | <elem1>...</elem1>
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| 22 | <elem2>...</elem2>
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| 23 | </mydoc></pre><p>The namespace value has to be an absolute URL, but the URL doesn't have to
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| 24 | point to any existing resource on the Web. It will bind all the element and
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| 25 | attributes with that URL. I suggest to use an URL within a domain you
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| 26 | control, and that the URL should contain some kind of version information if
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| 27 | possible. For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a
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| 28 | good namespace scheme.</p><p>Then when you load a file, make sure that a namespace carrying the
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| 29 | version-independent prefix is installed on the root element of your document,
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| 30 | and if the version information don't match something you know, warn the user
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| 31 | and be liberal in what you accept as the input. Also do *not* try to base
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| 32 | namespace checking on the prefix value. <foo:text> may be exactly the
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| 33 | same as <bar:text> in another document. What really matters is the URI
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| 34 | associated with the element or the attribute, not the prefix string (which is
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| 35 | just a shortcut for the full URI). In libxml, element and attributes have an
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| 36 | <code>ns</code> field pointing to an xmlNs structure detailing the namespace
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| 37 | prefix and its URI.</p><p>@@Interfaces@@</p><pre>xmlNodePtr node;
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| 38 | if(!strncmp(node->name,"mytag",5)
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| 39 | && node->ns
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| 40 | && !strcmp(node->ns->href,"http://www.mysite.com/myns/1.0")) {
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| 41 | ...
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| 42 | }</pre><p>Usually people object to using namespaces together with validity checking.
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| 43 | I will try to make sure that using namespaces won't break validity checking,
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| 44 | so even if you plan to use or currently are using validation I strongly
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| 45 | suggest adding namespaces to your document. A default namespace scheme
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| 46 | <code>xmlns="http://...."</code> should not break validity even on less
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| 47 | flexible parsers. Using namespaces to mix and differentiate content coming
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| 48 | from multiple DTDs will certainly break current validation schemes. To check
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| 49 | such documents one needs to use schema-validation, which is supported in
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| 50 | libxml2 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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