Publisher Summary In the Harmony process, architecture is defined to be the set of strategic design decisions that specify how the elements in the system are organized and interact. The key terms in the definition are “strategic” and “design.” In the Harmony process, design is all about optimization. The analysis model is driven primarily by the functional requirements of the system, and design is driven by the quality of service requirements and other optimality characteristics collectively known as “design criteria.” An analysis model may be optimized in almost infinitely different ways to achieve different optimization goals. For example, memory usage can be optimized at the expense of worst-case performance, or reusability can be optimized at the expense of development time. The analysis model specifies what must be present for the solution to be correct; design specifies a solution that is optimal against the criticality-weighted set of design criteria.