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<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">
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</style><title>Namespaces</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"> |    | The XML C parser and toolkit of GnomeNamespaces |
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| <center>Related links</center> | |
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recognizing namespace constructs in the input, and does namespace lookup
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automatically when building the DOM tree. A namespace declaration is
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associated with an in-memory structure and all elements or attributes within
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that namespace point to it. Hence testing the namespace is a simple and fast
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equality operation at the user level.I suggest that people using libxml2 use a namespace, and declare it in the
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root element of their document as the default namespace. Then they don't need
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to use the prefix in the content but we will have a basis for future semantic
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refinement and merging of data from different sources. This doesn't increase
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the size of the XML output significantly, but significantly increases its
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value in the long-term. Example:<mydoc xmlns="http://mydoc.example.org/schemas/">
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<elem1>...</elem1>
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<elem2>...</elem2>
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</mydoc>The namespace value has to be an absolute URL, but the URL doesn't have to
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point to any existing resource on the Web. It will bind all the element and
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attributes with that URL. I suggest to use an URL within a domain you
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control, and that the URL should contain some kind of version information if
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possible. For example, "http://www.gnome.org/gnumeric/1.0/" is a
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good namespace scheme.Then when you load a file, make sure that a namespace carrying the
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version-independent prefix is installed on the root element of your document,
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and if the version information don't match something you know, warn the user
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and be liberal in what you accept as the input. Also do *not* try to base
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namespace checking on the prefix value. <foo:text> may be exactly the
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same as <bar:text> in another document. What really matters is the URI
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associated with the element or the attribute, not the prefix string (which is
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just a shortcut for the full URI). In libxml, element and attributes have an
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ns field pointing to an xmlNs structure detailing the namespace
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prefix and its URI.@@Interfaces@@ xmlNodePtr node;
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if(!strncmp(node->name,"mytag",5)
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&& node->ns
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&& !strcmp(node->ns->href,"http://www.mysite.com/myns/1.0")) {
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...
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}Usually people object to using namespaces together with validity checking.
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I will try to make sure that using namespaces won't break validity checking,
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so even if you plan to use or currently are using validation I strongly
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suggest adding namespaces to your document. A default namespace scheme
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xmlns="http://...." should not break validity even on less
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flexible parsers. Using namespaces to mix and differentiate content coming
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from multiple DTDs will certainly break current validation schemes. To check
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such documents one needs to use schema-validation, which is supported in
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libxml2 as well. See relagx-ng and w3c-schema.Daniel Veillard </body></html>
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