In reply to sasi_8985:
You were mixing up the terms for child and parent. I recommend against using parent and child when referring to OOP inheritance. Parents create(construct) children and they are distinct objects from their parents. When you inherit property, that property becomes yours and all your property belongs to one object. Use base and extended.
The UVM uses terms parent and child to refer to relationships between objects when build a hierarchical tree/graph structure. The class uvm_component has a handle to its parent and handles to all its children so that you can traverse the hierarchical structure. This terminology is used in most programming languages and is independent of OOP.
You correct that if the parent argument is null when constructing any object derived for uvm_component, the UVM sets the parent to the uvm_top object.
I don't understand your second question, or what you are trying to understand. I'm not sure if going into the details of the UVM implemntation will be productive in this forum.