Top-down and bottom-up approaches originated in software development and have since been extended to other procedures. In the top-down approach an overview of the system is formulated, without going into detail for any part of it. Each part of the system is then refined by designing it in more detail.
In the context of a Foresight exercise, when a top-down approach is taken the process begins by aiming to achieve a clear vision of the whole project at the outset. The process is structured with formal methods. Usually small panels of experts drawn from different stakeholder groups work on information gathered from a wide range of sources. The opposite procedure, which starts by looking at the specific details and moves up towards a general overview, is known as the bottom-up approach.