Listing Vault SE322 · chapter 08 · Architecture Evaluation

Chapter 08 — Architecture Evaluation

Why architectures are evaluated, the three methods, and the nine ATAM steps with the outputs an evaluation is supposed to produce.

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Architecture Evaluation

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Purpose of Evaluation 4

  1. Check that decisions satisfy business goals and quality requirements
  2. Expose risks, sensitivity points, trade-off points and missing information
  3. Evaluate early and repeat when drivers or the architecture change
  4. Aim for informed decisions, not a pass/fail verdict

The Four Output Concepts 4

ConceptDefinition
RiskA decision or gap that endangers a quality goal — e.g. failover never tested under load
Non-riskA decision checked and found sound, with the reason recorded
Sensitivity pointA property where a change strongly affects one quality attribute
Trade-off pointA property that is a sensitivity point for two or more attributes at once

The Three Evaluation Methods 3

MethodFocusUse when
SAAMScenario-based modifiability and functionality; came firstThe question is how costly a set of planned changes will be
ATAMAll quality attributes and their interactions; generalized SAAMA finished architecture has competing quality goals
ARIDActive design review of an intermediate, unfinished designA partial design must be validated by the teams that will use it

ATAM — The Nine Steps 9

  1. Present the ATAM method
  2. Present the business drivers
  3. Present the architecture
  4. Identify the architectural approaches
  5. Generate the quality attribute utility tree
  6. Analyze the architectural approaches
  7. Brainstorm and prioritize scenarios
  8. Analyze the architectural approaches again (with the prioritized scenarios)
  9. Present the results

ATAM — Phases 3

  1. Preparation / Phase 1 — work with the core design team
  2. Evaluation / Phase 2 — widen to the broader stakeholder group
  3. Follow-up / Phase 3 — deliver the report and track the actions

ATAM — Participants 3

  1. The evaluation team and its roles
  2. Project decision makers
  3. Architecture stakeholders

ATAM — Outputs 7

  1. The utility tree
  2. The architectural approaches
  3. The prioritized scenarios
  4. Risks
  5. Non-risks
  6. Sensitivity points
  7. Trade-off points

Utility Tree Structure 4 levels

  1. Utility — the root
  2. Quality attribute — performance, availability, security, modifiability…
  3. Refinement — a narrower concern within that attribute
  4. Concrete scenario — a leaf, rated (importance, difficulty) such as (H,H)

Prioritization Rule 1

  1. (H,H) leaves are analyzed first — most business value and most architectural uncertainty

Scenario Parts Used in Evaluation 5

  1. Stimulus
  2. Environment
  3. Artifact
  4. Response
  5. Response measure

Analysis Discipline 4

  1. Trace each scenario through runtime and development structures
  2. Record the decisions each approach embodies and the questions asked about it
  3. Prototype or measure where reasoning alone is weak
  4. Keep assumptions and evidence visibly separate

Review Outcomes to Capture 5

  1. Risks and non-risks
  2. Risk themes grouped from related weaknesses
  3. Decisions made during the review
  4. Open questions
  5. Recommended experiments, each with an owner and a date