Daniel Veillard | 43d3f61 | 2001-11-10 11:57:23 +0000 | [diff] [blame] | 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd"> |
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| 13 | <title>Namespaces</title> |
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| 18 | <a href="http://www.gnome.org/"><img src="smallfootonly.gif" alt="Gnome 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> |
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| 21 | <h1>The XML C library for Gnome</h1> |
| 22 | <h2>Namespaces</h2> |
| 23 | </td></tr></table></td></tr></table></td> |
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Daniel Veillard | c948420 | 2001-10-24 12:35:52 +0000 | [diff] [blame] | 28 | <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr> |
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| 50 | <li><a href="namespaces.html">Namespaces</a></li> |
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Daniel Veillard | c948420 | 2001-10-24 12:35:52 +0000 | [diff] [blame] | 59 | </ul></td></tr> |
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Daniel Veillard | db9dfd9 | 2001-11-26 17:25:02 +0000 | [diff] [blame] | 69 | <li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li> |
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Daniel Veillard | 594cf0b | 2001-10-25 08:09:12 +0000 | [diff] [blame] | 71 | </ul></td></tr> |
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Daniel Veillard | c948420 | 2001-10-24 12:35:52 +0000 | [diff] [blame] | 74 | <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"> |
| 75 | <p>The libxml library implements <a href="http://www.w3.org/TR/REC-xml-names/">XML namespaces</a> support by |
| 76 | recognizing namespace contructs in the input, and does namespace lookup |
| 77 | automatically when building the DOM tree. A namespace declaration is |
| 78 | associated with an in-memory structure and all elements or attributes within |
| 79 | that namespace point to it. Hence testing the namespace is a simple and fast |
| 80 | equality operation at the user level.</p> |
| 81 | <p>I suggest that people using libxml use a namespace, and declare it in the |
| 82 | root element of their document as the default namespace. Then they don't need |
| 83 | to use the prefix in the content but we will have a basis for future semantic |
| 84 | refinement and merging of data from different sources. This doesn't increase |
| 85 | the size of the XML output significantly, but significantly increases its |
| 86 | value in the long-term. Example:</p> |
| 87 | <pre><mydoc xmlns="http://mydoc.example.org/schemas/"> |
| 88 | <elem1>...</elem1> |
| 89 | <elem2>...</elem2> |
| 90 | </mydoc></pre> |
| 91 | <p>The namespace value has to be an absolute URL, but the URL doesn't have to |
| 92 | point to any existing resource on the Web. It will bind all the element and |
| 93 | atributes with that URL. I suggest to use an URL within a domain you control, |
| 94 | and that the URL should contain some kind of version information if possible. |
| 95 | For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a good |
| 96 | namespace scheme.</p> |
| 97 | <p>Then when you load a file, make sure that a namespace carrying the |
| 98 | version-independent prefix is installed on the root element of your document, |
| 99 | and if the version information don't match something you know, warn the user |
| 100 | and be liberal in what you accept as the input. Also do *not* try to base |
| 101 | namespace checking on the prefix value. <foo:text> may be exactly the |
| 102 | same as <bar:text> in another document. What really matters is the URI |
| 103 | associated with the element or the attribute, not the prefix string (which is |
| 104 | just a shortcut for the full URI). In libxml, element and attributes have an |
| 105 | <code>ns</code> field pointing to an xmlNs structure detailing the namespace |
| 106 | prefix and its URI.</p> |
| 107 | <p>@@Interfaces@@</p> |
| 108 | <p>@@Examples@@</p> |
| 109 | <p>Usually people object to using namespaces together with validity checking. |
| 110 | I will try to make sure that using namespaces won't break validity checking, |
| 111 | so even if you plan to use or currently are using validation I strongly |
| 112 | suggest adding namespaces to your document. A default namespace scheme |
| 113 | <code>xmlns="http://...."</code> should not break validity even on less |
| 114 | flexible parsers. Using namespaces to mix and differentiate content coming |
| 115 | from multiple DTDs will certainly break current validation schemes. I will |
| 116 | try to provide ways to do this, but this may not be portable or |
| 117 | standardized.</p> |
| 118 | <p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p> |
| 119 | </td></tr></table></td></tr></table></td></tr></table></td> |
| 120 | </tr></table></td></tr></table> |
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