Agile Modeling Strategies
An important part of Iteration 0 is requirements and architectural envisioning because it enables you to gain critical information required to start the project successfully. For example, few organizations will fund a project unless the team can indicate what problem they intend to address, how they intend to do so, roughly how much it will cost, and roughly how long it will take. The team needs at least a high-level understanding of the requirements and a reasonable technical strategy; hence, the need for initial envisioning. I recently ran a survey within the agile community to explore this issue (the results are posted at www.ambysoft.com/surveys/practicesPrinciples2008.html) and found that 83 percent of respondents indicated that they very often, often, or sometimes performed requirements envisioning and 81 percent performed architectural envisioning at similar levels. Contrary to popular belief, agilists do in fact do up-front modeling.
It is during your initial requirements envisioning that you will identify high-level functional requirements, NFRs, and constraints. All forms of requirements will drive your architectural efforts, which occur iteratively in parallel with requirements envisioning. Initial envisioning is done at a high-level, the goal is to do just enough modeling to provide sufficient information to drive the initial decision making on your project. The goal is not to create detailed specifications because that would actually increase the risk, and the costs, of your project.
Although the initial envisioning efforts make you aware of the NFRs and constraints, you will discover that you very likely don't have the details that you require to fully address them. These details are captured on a JIT basis throughout construction via short model storming sessions with stakeholders. For example, you'll pull a functional requirement off the top of the stack that describes a change to an existing screen and supporting functionality behind that screen. As you explore the details of the functional requirement on a JIT basis with your stakeholder(s), you will also explore the cross-cutting NFRs and constraints that apply to it. The implication is that not only do the developers need to be aware of the NFRs and constraints, which the initial envisioning should have accomplished, they need to be sufficiently skilled to do so. More on this shortly.