Understanding the requirements of a problem is among the most difficult tasks that face a software engineer. When you first think about it, requirements engineering doesn't seem that hard. After all, doesn't the customer know what is required? Shouldn't the end-users have a good understanding of the features and functions that will provide benefit? Surprisingly, in many instances the answer to these questions is no. And even if customers and end-users are explicit in their needs, those needs will change throughout the project. Requirements engineering is hard.