How do architecture patterns and tactics interact? A model and annotation

Software architecture designers inevitably work with both architecture patterns and tactics. Architecture patterns describe the high-level structure and behavior of software systems as the solution to multiple system requirements, whereas tactics are design decisions that improve individual quality attribute concerns. Tactics that are implemented in existing architectures can have significant impact on the architecture patterns in the system. Similarly, tactics that are selected during initial architecture design significantly impact the architecture of the system to be designed: which patterns to use, and how they must be changed to accommodate the tactics. However, little is understood about how patterns and tactics interact. In this paper, we develop a model for the interaction of patterns and tactics that enables software architects to annotate architecture diagrams with information about the tactics used and their impact on the overall structure. This model is based on our in-depth analysis of the types of interactions involved, and we show several examples of how the model can be used to annotate different kinds of architecture diagrams. We illustrate the model and annotation by showing examples taken from real systems, and describe how the annotation was used in architecture reviews. Tactics and patterns are known architectural concepts; this work provides more specific and in-depth understanding of how they interact. Its other key contribution is that it explores the larger problem of understanding the relation between strategic decisions and how they need to be tailored in light of more tactical decisions.