what are the software requirement for complex systems?

Requirements for Complex Systems :

A system of any but the smallest size will
be decomposed into a hierarchy of
elements (partitioning):

 This is reflected at the requirement level by:
 

(1) Allocation: assigning requirements to
elements
 

(2) Flowdown: requirements which respond to the
allocated highel level requirements
 

(3) Traceability: keep track of the dependencies