Architecture Tradeoff Analysis Method (ATAM)
The Architecture Tradeoff Analysis Method (ATAM) is a method for evaluating software architectures relative to quality attribute goals.
ATAM evaluations expose architectural risks that potentially inhibit the achievement of an organization's business goals. The ATAM gets its name because it not only reveals how well an architecture satisfies particular quality goals, but it also provides insight into how those quality goals interact with each other—how they trade off against each other.
Business drivers and the software architecture are elicited from project decision makers. These are refined into scenarios and the architectural decisions made in support of each one. Analysis of scenarios and decisions results in identification of risks, non-risks, sensitivity points, and tradeoff points in the architecture. Risks are synthesized into a set of risk themes, showing how each one threatens a business driver.
The ATAM consists of nine steps:
- Present the ATAM. The evaluation leader describes the evaluation method to the assembled participants, tries to set their expectations, and answers questions they may have.
- Present business drivers. A project spokesperson (ideally the project manager or system customer) describes what business goals are motivating the development effort and hence what will be the primary architectural drivers (e.g., high availability or time to market or high security).
- Present architecture. The architect will describe the architecture, focusing on how it addresses the business drivers.
- Identify architectural approaches. Architectural approaches are identified by the architect, but are not analyzed.
- Generate quality attribute utility tree. The quality factors that comprise system "utility" (performance, availability, security, modifiability, usability, etc.) are elicited, specified down to the level of scenarios, annotated with stimuli and responses, and prioritized.
- Analyze architectural approaches. Based on the high-priority factors identified in Step 5, the architectural approaches that address those factors are elicited and analyzed (for example, an architectural approach aimed at meeting performance goals will be subjected to a performance analysis). During this step, architectural risks, sensitivity points, and tradeoff points are identified.
- Brainstorm and prioritize scenarios. A larger set of scenarios is elicited from the entire group of stakeholders. This set of scenarios is prioritized via a voting process involving the entire stakeholder group.
- Analyze architectural approaches. This step reiterates the activities of Step 6, but using the highly ranked scenarios from Step 7. Those scenarios are considered to be test cases to confirm the analysis performed thus far. This analysis may uncover additional architectural approaches, risks, sensitivity points, and tradeoff points, which are then documented.
- Present results. Based on the information collected in the ATAM (approaches, scenarios, attribute-specific questions, the utility tree, risks, non-risks, sensitivity points, tradeoffs), the ATAM team presents the findings to the assembled stakeholders.
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