Software Architecture

Architecture Tradeoff Analysis Method

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.

The ATAM is the leading method in the area of software architecture evaluation. An evaluation using the ATAM typically takes three to four days and gathers together a trained evaluation team, architects, and representatives of the architecture's various stakeholders.

Challenges

Most complex software systems are required to be modifiable and have good performance. They may also need to be secure, interoperable, portable, and reliable. But for any particular system

  • What precisely do these quality attributes such as modifiability, security, performance, and reliability mean?
  • Can a system be analyzed to determine these desired qualities?
  • How soon can such an analysis occur?
  • How do you know if a software architecture for a system is suitable without having to build the system first?

Description

A conceptual flow of the ATAM
A Conceptual Flow of the ATAM

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:

  1. 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.
  2. 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).
  3. Present architecture. The architect will describe the architecture, focusing on how it addresses the business drivers.
  4. Identify architectural approaches. Architectural approaches are identified by the architect, but are not analyzed.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.

The most important results are improved architectures. The output of an ATAM is an outbrief presentation and/or a written report that includes the major findings of the evaluation. These are typically

  • a set of architectural approaches identified
  • a "utility tree"—a hierarchic model of the driving architectural requirements
  • the set of scenarios generated and the subset that were mapped onto the architecture
  • a set of quality-attribute-specific questions that were applied to the architecture and the responses to these questions
  • a set of identified risks
  • a set of identified non-risks
  • a synthesis of the risks into a set of risk themes that threaten to undermine the business goals for the system

Benefits

  • clarified quality attribute requirements
  • improved architecture documentation
  • documented basis for architectural decisions
  • identified risks early in the life cycle
  • increased communication among stakeholders

The most important results are improved architectures. The ATAM aids in eliciting sets of quality requirements along multiple dimensions, analyzing the effects of each requirement in isolation, and then understanding the interactions of these requirements.

Who Would Benefit

Many people have a stake in a system's architecture, and all of them exert whatever influence they can on the architect(s) to make sure that their goals are addressed. For example, the users want a system that is easy to use and has rich functionality. The maintenance organization wants a system that is easy to modify. The developing organization (as represented by management) wants a system that is easy to build and that will employ the existing work force to good advantage. The customer (who pays the bill) wants the system to be built on time and within budget. All of these stakeholders will benefit from applying the ATAM. And needless to say, the architect is also a primary beneficiary.

Availability

The SEI has used this method to evaluate the software architectures of systems from many different application domains. The SEI is currently looking for organizations that would like to incorporate the ATAM as one of their routine software development practices.

The SEI can evaluate your architecture using the ATAM or qualify individuals to

An SEI-authorized ATAM evaluation is one that is led by an SEI-certified ATAM Leader and whose team is made up of individuals who have received the SEI ATAM Evaluator certificate.

For additional details or to arrange an ATAM evaluation for your organization, contact us at info@sei.cmu.edu.

Additional Information

Direct technical questions about ATAM to us using the link in the For more information box at the bottom of this page. To see a list of SEI-Certified ATAM Leaders, visit Find an SEI Partner Sponsored Individual and select "ATAM Leader (Certified)" from the drop-down list. You can also become certified to lead your own ATAM evaluations. For more information on becoming an SEI-Certified ATAM Leader, visit our certification page.

Software Architecture Training and Publications

Software Architecture Training at the SEI

Software Architecture Publications

Further Reading

SEI blog posts about the Architecture Tradeoff Analysis Method (ATAM)

Progress Toward an Organic Software Architecture Capability in the U.S. Army, Stephen Blanchette, Jr. & John K. Bergey

Categorizing Business Goals for Software Architectures
Rick Kazman & Len Bass

Evaluating Software Architectures: Methods and Case Studies
Paul Clements, Rick Kazman, & Mark Klein

Risk Themes Discovered Through Architecture Evaluations
Len Bass, Robert Nord, William Wood, & David Zubrow
 

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