This may be the most important chapter you write in the course of a solution development project!
While the project manager may have been issued a mission statement by the project’s sponsor and/or steering committee, this chapter is the architect’s mission statement. Of course it can’t contradict the project’s mission statement, but it can expand on it to include architectural priorities.
If you can get everyone in and behind the project to commit to a powerful mission statement, you are less likely to constantly get overruled every time there’s a disagreement about how to solve a problem. The architect is usually alone in wanting to adhere to best design principles in order to deliver a well-functioning and easily maintained system with as low cost-of-ownership as possible.
A typical project mission statement will state that ‘the project is supposed to build solution X in order replace solution Y no later than Z’. No mentioning of the quality, potential life span or maintainability etc. Which basically means you can get away with delivering a rubbish solution that needs to be replaced with 2-3 years!
So, the architectural mission statement could for example state that ‘solution Y is designed within given design constraints, adhering to design principles and meeting design goals, all of which ensuring a solution that is well-functioning, well-performing, and well-manageable’.
The constraints are as said given, but question those that risk sabotaging the stated mission. Chose design principles and set design goals to support the sated mission.
When others later question the rational for sticking to them, refer to the underlaying mission statement, which everyone has committed to, and win more battles that way!
Of, course, sometime real life gets in the way of doing what’s right – for now. But I find that it’s easier to convince others to accept enhancements and changes later, when I can argue that they are necessary to get the design back on track in accordance with the mission statement that everyone has committed to.