Namespaces are declared within an element's begin tag. The syntax for declaring a namespace looks like this:
<namespacePrefix:elementName xmlns:namespacePrefix = 'URL'>
This particular URL does not refer to a DTD or a schema. The URL doesn't even have to point to an existing file. Its purpose is to provide a unique name to associate with the elements and attributes in the XML document. The namespace can also be identified by a URI or a URN.
Because each URL, URI, or URN is unique, using a company's URL followed by additional text should create unique identifiers for each namespace. Here is an example of this format:
<?xml version="1.0"?>
<bill:message xmlns:bill='http://www.northwindtraders.com/bill'>
<bill:date>1/1/2002</bill:date>
<bill:body>Your current balance is $1,999,999.00. Please pay
immediately. Thank you.</bill:body>
</bill:message>
You can also declare more than one namespace in an element's begin tag, as shown here:
<?xml version="1.0"?>
<bill:message xmlns:bill='http://www.northwindtraders.com/bill'
xmlns:body='http://www.northwindtraders.com/message'>
<bill:date>1/1/2002</bill:date>
<body:body>Your current balance is $1,999,999.00. Please pay
immediately. Thank you. </body:body>
</bill:message>
In this example, the message element contains two namespace declarations: bill and body. The bill namespace is used to define the message element and the date child element. The body namespace is used to define the body child element.
