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Software Architecture Guide

Replaceability

Explanation

Section titled “Explanation”

Replaceability describes how well one product can stand in for another specified product. The replacement must serve the same purpose in the same environment. ISO/IEC 25010 defines it this way (see the article on the ISO/IEC 25010 Product Quality Model).

Where it sits in the quality model. In the 2023 model, replaceability belongs to Flexibility. Flexibility is how well a product adapts to changes in its requirements, contexts of use or system environment. Replaceability shares that group with adaptability, scalability and installability.

Why it matters. Replaceability reduces lock-in risk. Lock-in means being stuck with the present product. With good replaceability, other software products can be used in its place.

Do not confuse it with its neighbors. The Q42 quality model separates three terms by what moves:

  • Portability changes the environment.
  • Replaceability changes the product.
  • Interchangeability changes a component inside the product.

Do not assume equivalence. A matching interface does not prove that a candidate can replace the current product. Q42 says equivalence should be established empirically. One way is to run an evaluation suite against the candidate.

Example

Section titled “Example”

A team uses one product to send customer emails. A cheaper product appears. The team does not take it on trust that the new product works the same. They run their existing set of evaluation checks against the candidate. The results show whether it can take over the same purpose in the same environment.

Trade-offs

Section titled “Trade-offs”

The available facts do not describe the costs of making a product replaceable. They do show one pitfall: judging a replacement by interface compatibility alone. Plan for empirical checks of the candidate, and expect that effort as part of any replacement.

Checks

Section titled “Checks”
  • The document states which specified product a replacement must stand in for, and for what purpose and in which environment.
  • The document says how equivalence of a replacement candidate will be established, for example by running an evaluation suite, rather than assuming it from interface compatibility.
  • The document names lock-in risks and says which other products could be used in place of the present one.
  • The document makes clear whether a change affects the environment (portability), the whole product (replaceability) or a component inside it (interchangeability).
Section titled “Related”

Sources

Section titled “Sources”