The top-down and bottom-up approaches originated in the software development field, but have since been extended to other areas. In the bottom-up approach the individual parts of the system are first specified in detail. These parts are then linked together to form larger components, which are in turn assembled until a complete system is formed.
In the context of a Foresight exercise, the bottom-up approach refers to a situation where the process emerges from the different bits and pieces assembled along the way. The overall direction and coverage of the exercise is not completely defined at the outset and strong emphasis is placed on interaction between participants.
The process of information gathering as well as the dissemination and implementation of the results are themselves subject to discussion. Following the opposite procedure constitutes a top-down approach.