Analyzing%20an%20Architecture

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Analyzing an Architecture
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Why analyze an architecture?

• Decide whether it solves the problem
• Compare to other architectures
• Assess what needs to change, given some major
  requirements change
• Find a problem

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Methods

• ATAM Architecture Trade-off Analysis
• CBAM Cost Benefit Analysis
• Architecture Review

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ATAM
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ATAM Participants

• Evaluation Team
• Project Decision Makers
• Sponsor, Customer, Management
• Architecture Stakeholder
• Developers, Users, Testers, etc.

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Evaluation Team

• Team Leader
• Evaluation Leader
• Scenario Scribe
• Proceedings Scribe
• Timekeeper
• Process Observer
• Process Enforcer
• Questioner

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Outputs

• Concise presentation of the Architecture
• Articulation of Business Goals
• Quality Requirements collection of scenarios
• Mapping of Architectural decisions to qualities
• Identified sensitivity and trade-off points
• Set of risks and non-risks
• Set of risk themes

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Phases of ATAM

• 0 - Partnership and Preparation
• 1 Evaluation 1 -- 1 day
• 2 TO 3 WEEKS BREAK HERE!
• 2 Evaluation 2 2 days
• 4 Follow-up -- 1 week

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Evaluation Steps Phase 1

• 1 - Present the ATAM
• 2 - Present Business Drivers
• Most important functions
• Constraints technical, economic, political
• Business goals
• Major stakeholders
• Architectural drivers

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Evaluation Steps

• 3 Present Architecture (20 slides 60 minutes)
• 4 Identify Architectural Approaches
• 5 Quality Attribute Utility Tree

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Quality attribute utility tree

• Top level quality attributes
• Second level attribute sub-categories (or,
  scenario groupings if you think bottom-up)
• Third level quality attribute scenarios
• For each scenario, two priority rankings (H/M/L)
• Importance
• Architects estimate of difficulty
• See pp 296-297

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Scenario priority hierarchy (Dons)
HH Top
HM, MH Second level
MM Time permitting
HL, ML, LL Ignore (you won't have time anyway, and they aren't hard to build)
LH, LM Why would you implement this in the first place?
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Evaluation Steps

• 6 Analyze Architectural Approaches
• Focus on top priority scenarios first, then 2nd
  level,
• Understand the architectural decisions made for
  the scenario, and the consequences
• For each architectural decision, generate lists
  of
• Sensitivity points (scenarios influenced by the
  decision)
• Tradeoff points (one scenario helped, another one
  hurt)
• For each sensitivity point and each tradeoff,
  decide whether it is a risk or non-risk

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Sensitivities and tradeoffs examples

• Sensitivities
• Configuration files good for modifiability
• Virtual machine good for portability
• Virtual machine bad for performance
• Virtual machine is also a tradeoff point, because
  it is good for at least one attribute and bad for
  at least one other

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Evaluation Steps Phase 2

• 7 Brainstorm and prioritize scenarios
• 8 - Analyze Architectural Approaches
• 9 Present Results

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CBAM
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CBAM

• Goal of CBAM is quantifying decisions
• Utility a measure of value
• Cost to implement a given strategy
• Use outputs of ATAM
• This is a subjective process!

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Scenario

• For each scenario of ATAM
• Generate a set of scenarios
• The set has a range of responses
• The response measure needs to be quantified

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Assign Utility Values

• This can be hard!
• Look at plots in text (pg. 311)
• Start by establishing worst-case and best-case
  limits (0 and 100)
• They also tried to find a current and desired
  value

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Priorities

• Prioritize the scenarios in order first
• The add a weight for each one

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Architectural Strategies

• Expected value of the response
• (Interpolate on the plot)
• Effect on other attributes
• Cost to implement

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Benefit

• Bi Sj (bi,j Wj)
• bi,j expected change in utility with respect to
  scenario j as a result of using strategy i.
• W is weight of scenarios

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ROI

• R B / C

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Summary

• ATAM and CBAM provide structure
• CBAM can be hard, since quantification is called
  for!
• Next week we consider a less structured
  alternative.