I have seem the terms top-down bottom-up approach,top-down bottom-up models,top-down bottom-up causation in many papers. I am bit confused.Are they really same or how can we define them ?
If you're talking about the philosophy of science, 'top-down' approaches start with theory and then tries to produce observations through experimentation that validate that theory. 'Bottom-up' approaches begin by collating observations in the real world and trying to construct a theory from them. The terms are more or less synonymous with 'theory-driven' and 'data-driven'. In the philosophy of science it's generally seen as a chicken-or-egg question, since both approaches are frequently used in practice. It's mainly an academic question about which approach has primacy.