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XML Namespaces

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  1. XML Namespaces Kanda Runapongsa (krunapon@kku.ac.th) Dept. of Computer Engineering Khon Kaen University

  2. What are Namespaces? • Namespaces are a simple and straightforward way to distinguish names used in XML documents, no matter where they come from • [W3C Definition] An XML namespace is a collection of names, identified by a URI reference, which are used in XML documents as element types and attribute names. 168493: XML and Web Services (II/2546)

  3. <h:html xmlns:xdc="http://abc.com/books" xmlns:h="http://www.w3.org/HTML"> <h:head> <h:title>Book Review</h:title> </h:head> <h:body> <xdc:bookreview> <xdc:title>XML</xdc:title> </xdc:bookreview> </h:body> </h:html> 168493: XML and Web Services (II/2546)

  4. Namespaces by Example • In the example, the elements prefixed with xdc are associated with a namespace whose name is http://abc.com/books • Those prefixed with h are associated with a namespace whose name is http://www.w3.org/HTML 168493: XML and Web Services (II/2546)

  5. Prefixes • Prefixes are linked to the full names using the attributes on the top element whose names begin xmlns: • Prefixes are just shorthand placeholders for the full names • The full names are URLs, i.e. Web addresses 168493: XML and Web Services (II/2546)

  6. Why Namespaces? • Book-review tags and HTML tags are all mixed up together • Need to be sure that we’re finding the book titles, not the HTML page titles • Can be done by processing only <title> tags that are in the http://abc.com/books namespace 168493: XML and Web Services (II/2546)

  7. Namespace Defaulting • Previously, we have all those prefixes and colons cluttering up the tags • We can declare a default namespace and leave out some prefixes • Anything without a prefix is assumed to be in the default namespace • A default namespace is considered to apply to the element where it is declared and to all elements with no prefix 168493: XML and Web Services (II/2546)

  8. <html xmlns:xdc="http://abc.com/books" xmlns="http://www.w3.org/HTML"> <head> <title>Book Review<title> </head> <body> <xdc:bookreview> <xdc:title>XML</xdc:title> </xdc:bookreview> <body> </html> 168493: XML and Web Services (II/2546)

  9. Namespace Defaulting (Cont.) • The default namespace can be set to the empty string • This has the same effect as having no default namespace • Note that default namespaces do not apply directly to attributes 168493: XML and Web Services (II/2546)

  10. Default Namespaces <!--the default namespace is now that of HTML -->  <table xmlns='http://www.w3.org/HTML'>   <th><td>Name</td></th>    <tr>      <!- no default namespace inside table cells -->     <td><brandName xmlns="">Huntsman</brandName></td> … 168493: XML and Web Services (II/2546)

  11. Attributes: Example 1 <x xmlns:n1="http://www.w3.org"    xmlns:n2=“http://www.w3.org”>  <e1  a="1"     a="2" />  <e2 n1:a="1"  n2:a="2" /> </x> • Is the start tag of e1 legal? • Is the start tag of e2 legal? 168493: XML and Web Services (II/2546)

  12. Attributes: Example 2 <x xmlns:n1="http://www.w3.org"    xmlns="http://www.w3.org" >  <e3 a="1"     b="2" />  <e4 a="1"     n1:a="2" /> </x> • Is the start tag of e3 legal? • Is the start tag of e4 legal? 168493: XML and Web Services (II/2546)

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