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Software Architecture Guide

Quality Attribute Coverage in Bass et al.

Explanation

Section titled “Explanation”

The SEI model is a short list of quality attributes. The arc42 quality model site counts only 10 top-level areas. ISO 25010 has about 40 terms. The arc42 author calls the SEI model a great simplification of the somewhat bloated ISO model.

Where the two models differ

  • Deployability. ISO 25010 (2011) lacks operational or DevOps qualities. Bass et al. treat deployability as a full attribute.
  • Safety. The 2011 ISO overview left out safety (safety of life and health, physical integrity). The 2022 draft adds it. Bass et al. have a dedicated safety chapter.
  • Energy efficiency. ISO 25010 groups time behavior, resource utilization and capacity under performance efficiency. Energy use would fit there as a resource concern.
  • Compatibility. ISO 25010 lists compatibility (co-existence and interoperability) as a characteristic. Bass et al. have no chapter with that name. Integrability is the nearest match.
  • Usability and performance. These map onto ISO’s interaction capability and performance efficiency.

Scenarios

Bass et al. coined “quality attribute scenarios.” A scenario is a structured way to write a quality requirement. It has six elements: source, stimulus, artifact, environment, response and metric. See the article Quality Attribute Scenario.

Using the coverage

You can use the 10 areas as a short checklist when choosing quality goals. If your system needs something the list lacks, such as compatibility, check the larger ISO list as well.

Example

Section titled “Example”

A team builds an online ordering service and wants quality goals. They start from the short list and pick performance and deployability, because they release often. Then they scan the ISO list. They notice the service must work with partner systems. They add that need as an integrability goal, the nearest match in the short list.

Trade-offs

Section titled “Trade-offs”

Benefits. A short list is easy to learn and use. It also includes deployability and safety, which ISO 25010 (2011) lacked.

Limits.

  • The short list leaves out some ISO topics, so it can hide needs such as compatibility.
  • Critics say deployability suits highly automated online and mobile systems. It suits embedded and real-time systems less, since they are deployed less often and with less automation. They propose “operable” as a top-level attribute, with deployable as a sub-goal.
  • Critics also say the six-part scenario template is a poor fit for agile work, because of redundancy and effort.

Checks

Section titled “Checks”
  • Quality goals were checked against both a short attribute list and the larger ISO 25010 list, so topics such as compatibility are not missed.
  • Deployability is considered, or its omission is justified, for the type of system (e.g., embedded systems deploy less often).
  • Safety is considered as a quality goal where physical harm is possible.
  • Key quality requirements are written as scenarios with source, stimulus, artifact, environment, response and metric.
Section titled “Related”

Sources

Section titled “Sources”