Understanding Namespace Context

[Yogs Kumar]

Hello Everyone,

I am trying to understand what exactly is a Namespace Context and request your help in this regard.

I am trying to write a simple REST service using Provider/Dispatcher model and using XPATH to traverse the request Source.
There is a statement which sets the NameSpaceContext for the XPATH object.I understand the concept of namespace which is done in order to avoid XML name collision and for clear identification of XML elements.

What exactly is this namespace context?Why is it necessary for both client and service to use the same namespace URI for the service to work correctly,also if client and service needs to use the same namespace URI,who provides the format or the URI to the client in cases of REST services.