Alert for user of Purchase Request Created or Changed to another user .

Hi Expert ,

If any USER created a Purchase Request and if that user is amendments (made changes ) on Purchase Request, so X user get an alert and

If X user created a Purchase Request , if anyone made changes(amendments) in that Purchase Request it should give an alert to X user. in standard only we can give for add mode only .

how to get this .is it possible by Query ........??

Thanks

Sarvesh Gupta