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Daniel Veillard8f40f1e2002-08-28 21:18:45 +0000[diff] [blame]19<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>
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22<h1>The XML C library for Gnome</h1>
23<h2>Namespaces</h2>
24</td></tr></table></td></tr></table></td>
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91<p>The libxml library implements <a href="http://www.w3.org/TR/REC-xml-names/">XML namespaces</a> support by
Daniel Veillard63d83142002-05-20 06:51:05 +0000[diff] [blame]92recognizing namespace constructs in the input, and does namespace lookup
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]93automatically when building the DOM tree. A namespace declaration is
94associated with an in-memory structure and all elements or attributes within
95that namespace point to it. Hence testing the namespace is a simple and fast
96equality operation at the user level.</p>
97<p>I suggest that people using libxml use a namespace, and declare it in the
98root element of their document as the default namespace. Then they don't need
99to use the prefix in the content but we will have a basis for future semantic
100refinement and merging of data from different sources. This doesn't increase
101the size of the XML output significantly, but significantly increases its
102value in the long-term. Example:</p>
103<pre>&lt;mydoc xmlns=&quot;http://mydoc.example.org/schemas/&quot;&gt;
104 &lt;elem1&gt;...&lt;/elem1&gt;
105 &lt;elem2&gt;...&lt;/elem2&gt;
106&lt;/mydoc&gt;</pre>
107<p>The namespace value has to be an absolute URL, but the URL doesn't have to
108point to any existing resource on the Web. It will bind all the element and
Daniel Veillardc0801af2002-05-28 16:28:42 +0000[diff] [blame]109attributes with that URL. I suggest to use an URL within a domain you
110control, and that the URL should contain some kind of version information if
111possible. For example, <code>&quot;http://www.gnome.org/gnumeric/1.0/&quot;</code> is a
112good namespace scheme.</p>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]113<p>Then when you load a file, make sure that a namespace carrying the
114version-independent prefix is installed on the root element of your document,
115and if the version information don't match something you know, warn the user
116and be liberal in what you accept as the input. Also do *not* try to base
117namespace checking on the prefix value. &lt;foo:text&gt; may be exactly the
118same as &lt;bar:text&gt; in another document. What really matters is the URI
119associated with the element or the attribute, not the prefix string (which is
120just a shortcut for the full URI). In libxml, element and attributes have an
121<code>ns</code> field pointing to an xmlNs structure detailing the namespace
122prefix and its URI.</p>
123<p>@@Interfaces@@</p>
124<p>@@Examples@@</p>
125<p>Usually people object to using namespaces together with validity checking.
126I will try to make sure that using namespaces won't break validity checking,
127so even if you plan to use or currently are using validation I strongly
128suggest adding namespaces to your document. A default namespace scheme
129<code>xmlns=&quot;http://....&quot;</code> should not break validity even on less
130flexible parsers. Using namespaces to mix and differentiate content coming
131from multiple DTDs will certainly break current validation schemes. I will
132try to provide ways to do this, but this may not be portable or
133standardized.</p>
Daniel Veillard3f4c40f2002-02-13 09:19:28 +0000[diff] [blame]134<p><a href="bugs.html">Daniel Veillard</a></p>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]135</td></tr></table></td></tr></table></td></tr></table></td>
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