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Software Architecture Guide

Tactic Trade-off Balancing

Explanation

Section titled “Explanation”

Quality goals often pull against each other. A choice that helps one goal can cost another. Tactic trade-off balancing is the work of handling that conflict on purpose. (See Architectural Tactic and Quality Attribute Trade-off for the basics.)

Rank the goals first. The ATAM method (Architecture Tradeoff Analysis Method) evaluates an architecture against its quality goals. It also shows how those goals interact and conflict. ATAM uses a utility tree for ranking. This is a tree of the requirements that drive the architecture, and it helps the team prioritize quality goals. With a ranking, a conflict has an answer to start from.

Find the collision points. In its analysis step, ATAM names three things: architectural risks, sensitivity points and trade-off points. Sensitivity Point and Trade-off Point have their own articles.

Expect surprises. A review of tactics for big data security calls for more research on trade-offs and dependencies among tactics. So these interactions are not well understood. Teams should not assume that tactics combine without friction.

Write the choice down. arc42 is a documentation template. Its solution strategy section holds the core decisions, including how the key quality goals are achieved. arc42 asks you to explain why you decided that way. It recommends one consolidated table that ties each quality goal to the decisions that follow from it. Section 9 asks for important decisions with their rationale, so stakeholders can retrace them. It also asks you to list all consequences, not only the positive ones. A trade-off that stays unrecorded is easy to forget.

Example

Section titled “Example”

A team ranks its quality goals and puts one goal at the top. It picks a tactic for that goal. In review, the team marks a trade-off point where the choice affects a lower-ranked goal. It then adds a row to its quality goal table. The row names the goal, the decision and the cost. It also lists that cost among the consequences in its decision record.

Trade-offs

Section titled “Trade-offs”

Balancing takes effort: ranking goals, running an evaluation and writing down consequences all cost time. Because interactions among tactics are not well understood, some side effects will only show up late. Writing down all consequences, including the negative ones, makes the compromises visible to stakeholders. That is the purpose of the practice.

Balancing tactics: rank goals, choose, analyze, record, and adjust.

Diagram source 
flowchart LR
  A[Quality goals] --> B[Rank in utility tree]
  B --> C[Choose tactics]
  C --> D[Analyze risks, sensitivity and trade-off points]
  D --> E[Record decisions and consequences]
  D -.->|adjust| C

Checks

Section titled “Checks”
  • Quality goals are ranked, for example in a utility tree, so conflicts can be settled by priority.
  • Trade-off points and sensitivity points found in the analysis are identified.
  • The solution strategy ties each key quality goal to the decisions made for it, ideally in one table.
  • Each important decision states its rationale, so stakeholders can retrace it.
  • Decision records list all consequences, including the negative ones.
Section titled “Related”

Sources

Section titled “Sources”