Explanation for top down and bottom up concepts in simple English?

Answer 1

Top down design is the philosophy that you start with the highest level of the system or program design. You define that functionality, perhaps writing stub or dummy routines for each of the next level designs so you can debug and test the top level. Then you proceed to the next level. You repeat the design and debug cycle at that level. If you top level design was adequate and correct, which it should be because you don't really want to go back up and make changes, then focus is only on the second level design. You repeat this process, going further and further down, until you complete the design and coding of the entire system. Assuming that each level of design is correct, it is possible to assign multiple parts of each level to different engineers. So long as the defined interface and requirements of that level are adequately provided, this method works well, and allows you to finish the overall design is less time than it would take one engineer to complete. <><><><><><> Bottom up design is the reverse. You start with the lowest levels of implementation, design and debug them, and then proceed upwards towards the top. This method can also work, but there is greater risk of needing to go back and correct some "missing thing" at one of the lower levels. It is usually effective when the whole system design is known at once, such as in a small implementation that one engineer can handle alone.