doubts about IR

1.how to delete name space in integration repository ?

2. when i am activating my objects in change list in IR i am getting name space is not defined in your software component version. what is this error how to overcome..

3. what is the need of adapter metadata in IR..

and communication channel after it in IR..

4.what is the diff between http://"namespace"

urn:"namespace"

could any one plz help me in this regard..