CopperSpice API: XML Namespaces

Using the CsXml library requires a basic understanding of XML namespaces. The following is only a brief introduction.

Namespaces are a were introduced into XML to allow a modular design to assist with resolving naming conflicts within XML documents. Namespaces are defined using a URI like http://www.example.com/placeholder/book/. This does not mean data is available at this address, the URI is simply used to provide a unique name.

Example 1

There are three different places where the name title is used. When processing this document you will encounter problems because every use of title should be displayed in a different manner. The solution is to have some way of identifying the first occurrence as the "title of a book" and distinguish it from the "chapter title".

<document>
<book>
   <title>A Brief History of Time</title>
   <author title="CBE" name="Stephen Hawking"/>
 
   <chapter>
      <title>Our Picture of the Universe</title>
   </chapter>
 
</book>
</document>

Example 2

In the following example the prefix book is a namespace which is applied to the title tag. Before a namespace can be used it must be declared.

<document xmlns:book = "http://example.com/placeholder/book/">   <!-- opens a document tag, declares a namespace -->
 
   <book:title>A Brief History of Time</book:title>

Example 3

A namespace is declared with "xmlns: followed by some text". This namespace can then be applied to elements and attributes by using the text followed by a colon as a prefix. In this example there are two declared namespaces. The first one uses a prefix of book and is then used by specifying book:title or book:author. The default namespace is used for bookX and chapterX.

The default namespace applies only to elements without a prefix. There is no default namespce for an attribute.

<document xmlns:book = 'http://example.com/xml/book/'
          xmlns      = 'http://example.com/xml/default/' >
 
<bookX>
  <book:title>A Brief History of Time</book:title>
 
  <book:author xmlns:placeholder = 'http://example.com/xml/default/'
               title="CBE"
               placeholder:title="FRSA"
               name="Stephen Hawking"/>
 
  <chapterX>
     <title>Our Picture of the Universe</title>
  </chapterX>
 
</bookX>
 
</document>

The placeholder namespace has the same namespace URI as the default namespace. The following explains why this namespace was added in the book:author element.

attributes without a prefix do not belong to any XML namespace, not even to the default namespace
omitting the prefix would lead to a conflict
writing it as xmlns:title would declare a new namespace with the prefix title instead of applying the default xmlns namespace

More information on XML namespaces can be found at http://www.w3.org/TR/REC-xml-names/.

Conventions Used in the CopperSpice XML Documentation

The following terms are used to distinguish the parts of names within the context of namespaces.

qualified name: Name as it appears in the document, in the above example book:title is a qualified name
namespace prefix: In a qualified name it is the part to the left of the colon, book is the namespace prefix in book:title
local part or local name: Appears to the right of the colon, title is the local part of book:title
namespace URI: Uniform Resource Identifier is a unique identifier for a namespace, it is similar to a URL but does not require data to be accessible by the given protocol at the named address

Elements without a colon like chapterX do not have a namespace prefix. In this case the local part and the qualified name are identical.