1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3 <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><link rel="SHORTCUT ICON" href="/favicon.ico" /><style type="text/css"> 4 TD {font-family: Verdana,Arial,Helvetica} 5 BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em} 6 H1 {font-family: Verdana,Arial,Helvetica} 7 H2 {font-family: Verdana,Arial,Helvetica} 8 H3 {font-family: Verdana,Arial,Helvetica} 9 A:link, A:visited, A:active { text-decoration: underline } 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%" 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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 11 recognizing namespace constructs in the input, and does namespace lookup 12 automatically when building the DOM tree. A namespace declaration is 13 associated with an in-memory structure and all elements or attributes within 14 that namespace point to it. Hence testing the namespace is a simple and fast 15 equality operation at the user level.</p><p>I suggest that people using libxml2 use a namespace, and declare it in the 16 root element of their document as the default namespace. Then they don't need 17 to use the prefix in the content but we will have a basis for future semantic 18 refinement and merging of data from different sources. This doesn't increase 19 the size of the XML output significantly, but significantly increases its 20 value in the long-term. Example:</p><pre><mydoc xmlns="http://mydoc.example.org/schemas/"> 21 <elem1>...</elem1> 22 <elem2>...</elem2> 23 </mydoc></pre><p>The namespace value has to be an absolute URL, but the URL doesn't have to 24 point to any existing resource on the Web. It will bind all the element and 25 attributes with that URL. I suggest to use an URL within a domain you 26 control, and that the URL should contain some kind of version information if 27 possible. For example, <code>"http://www.gnome.org/gnumeric/1.0/"</code> is a 28 good namespace scheme.</p><p>Then when you load a file, make sure that a namespace carrying the 29 version-independent prefix is installed on the root element of your document, 30 and if the version information don't match something you know, warn the user 31 and be liberal in what you accept as the input. Also do *not* try to base 32 namespace checking on the prefix value. <foo:text> may be exactly the 33 same as <bar:text> in another document. What really matters is the URI 34 associated with the element or the attribute, not the prefix string (which is 35 just a shortcut for the full URI). In libxml, element and attributes have an 36 <code>ns</code> field pointing to an xmlNs structure detailing the namespace 37 prefix and its URI.</p><p>@@Interfaces@@</p><pre>xmlNodePtr node; 38 if(!strncmp(node->name,"mytag",5) 39 && node->ns 40 && !strcmp(node->ns->href,"http://www.mysite.com/myns/1.0")) { 41 ... 42 }</pre><p>Usually people object to using namespaces together with validity checking. 43 I will try to make sure that using namespaces won't break validity checking, 44 so even if you plan to use or currently are using validation I strongly 45 suggest adding namespaces to your document. A default namespace scheme 46 <code>xmlns="http://...."</code> should not break validity even on less 47 flexible parsers. Using namespaces to mix and differentiate content coming 48 from multiple DTDs will certainly break current validation schemes. To check 49 such documents one needs to use schema-validation, which is supported in 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> 51
