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Software Architecture Guide

Standard Quality Attribute List

Explanation

Section titled “Explanation”

A standard quality attribute list names the qualities a system may need, such as the ones in ISO 25010 (see ISO/IEC 25010 Product Quality Model).

Shared vocabulary. The words people use for qualities vary with the author’s perspective. A common list gives everyone the same terms.

Known weaknesses. Critics of ISO 25010 point out several problems:

  • It builds a generic taxonomy (a structured set of terms) of almost 40 terms. The critic argues fewer terms would have been better.
  • Some terms overlap. Maintainability and flexibility have definitions that are too similar.
  • Placement is inconsistent. Adaptability also relates to maintainability, but the standard files it only under portability.
  • Any strict hierarchy of qualities can be disputed.

Gaps. Scalability was missing from the 2011 version. The 2022 draft added it under flexibility. Operational or DevOps qualities such as deployability are also missing. So no standard list is complete.

Names are not requirements. Words like “availability,” “security,” and “usability” are still ambiguous. A quality attribute scenario makes a requirement concrete. It lets you decide whether the requirement is fulfilled, and it should be specific and measurable (see Quality Attribute Scenario). About ten scenarios are manageable for most systems.

Example

Section titled “Example”

A team building an online shop reads through a standard list during requirements gathering. They notice nobody has talked about handling many visitors at once. They write one scenario that states what load the shop must handle and how that is judged. The list prompted the question. The scenario made it precise.

Trade-offs

Section titled “Trade-offs”

A standard list is a starting point, not a finished answer. It can be incomplete, it can overlap with itself, and it can lead to arguments about where a term belongs. Those arguments cost effort without improving the system. The list also gives no measures. Scenarios and deeper analysis must supply the precision.

Checks

Section titled “Checks”
  • Quality attribute names in the document are backed by scenarios that are specific and measurable.
  • The number of quality scenarios is kept manageable, around ten for most systems.
  • Qualities missing from the standard list, such as deployability, were considered where relevant.
Section titled “Related”

Sources

Section titled “Sources”