XML namespaces provide a simple method for qualifying element and attribute names used in Extensible Markup Language documents by associating them with namespaces identified by URI references.

Namespaces enable you to mix, in one XML document, element (and sometimes attribute) names from more than one XML vocabulary. Let's assume you've got a document in some vocabulary which looks, in part, like the following:
<furniture>
<table material="mahogany" type="dining"/>
<chair material="mahogany" type="dining"/>
<chair material="mahogany" type="dining"/>
<lamp material="brass" type="chandelier"/>
</furniture>

There is many probability that the element's name already exists when you are creating new elements. Here one example in health related XML document that included XHTML (that's HTML that is also valid XML).

Now we have two very different elements that want to use the same name: body. The solution to such type of problem is creation of XML Namespaces, which will differentiate between these similarly named elements!

The XML namespace is a reserved XML attribute that you place in an XML tag. The reserved attribute is actually a prefix that you attach to any namespace . This attribute prefix is "xmlns:", which stands for XML NameSpace. The colon is used to separate the prefix from your namespace that you are creating.

Every XML attribute must be set equal to something. xmlns must have a unique value which is not present in another namespace of whole document. What is the more commonly used URL.

We will be using the W3C's XHTML URL and a made up URI(Uniform Resource Identifier) for our second body element for rectify the overlap in our health XML document. Both the namespace attribute and its use in our document has been highlighted in blue.

We have solved the overlapping problem by placing a namespace prefix before our elements !