WSDL definitions

[CSG]

Hi All,

I have a simple question that I'm sure someone can explain to me. A
wsdl file starts off like:

<definitions name="Hello World"
targetNamespace="http://hello.wsdl"
xmlns:tns="http://hello.wsdl"
etc

My question is why do we a "targetNamespace" field and a "xmlns:tns"
field. Are they always the same? What's the difference between them?
Do we always have to have both?

Thanks

Colin