When we plan to design a software we need to focus certain things. Here are some important points we can go through. Functional Decomposition: Functional decomposition is natural way to deal with complexity. The challenges with this approach: to dealing with change and bugs originate with changes to code. Low cohesion, tight coupling Focus on function leads to a cascade of changes from which it is difficult to escape. The Problem of Requirements: Requirements always change. Requirements are incomplete. Requirements are usually wrong. Requirements (and users) are misleading. Requirements do not tell the whole story. Deal with Changes(Use Functional Decomposition): Shift responsbility from yourself to