Keeping in mind the characteristics outlined on the left side of the chart, we need to examine three terms — envisioning, requirements and user stories — all of which are integral elements of agile project management. In short, the envisioning process focuses on the content ("vision") of the project, including the purpose of the project and what it is expected to accomplish. The term requirement focuses on understanding the user's (client's) needs to solve a problem or achieve a solution or objective. A focus on requirements is usually the function of a business analysis. As outlined in the IIBA® Business Analysis Body of Knowledge® (BABOK® Guide), there are four categories of requirements with two sub-categories: