I have 3 object and group. Added an empty and parent to it. Holding the empty i can move the complete group. I can select the group and empty and press shit+D it duplicate. But how can i duplicate the complete group made with the empty in complex scene. When i select the empty i can just move complete group but when press shift+D it duplicate only the empty not the object which are parent to it. For example given below.
It is called Dupligroup. After assigning a group to an object/s, add an empty and go to the object properties. Under duplication you will find a group option, enable it and then select the group. Every object in the group (and others added later) will be duplicated around the empty.