Comment by fluoridation

I would argue that the act that makes a piece of software "derivative" of another is not loading them both onto the same address space (since that's a symmetric relation anyway), but whether making one depend on the other having a specific behavior. If A.so provides foo(int) with some contract C and B.so depends on an implementation of foo(int) that matches the contract C, then arguably B.so is derivative of A.so, and the more facilities A.so provides and B.so assumes are available, the stronger that argument becomes. Whether the way A.so and B.so communicate is through a calling convention, a pipe, or a network connection, is largely an implementation detail.