You can find all kinds of information on these on google. Top down is typically thought of as breaking your problem into subproblems, then breaking these subproblems into further subproblems until you have methods/functions that do one thing well. Bottom up is a bit harder to explain, here is a link that I think does an ok job, but you're better off researching it yourself. http://nothing.tmtm.com/2002/06/bottom-up-programming/