Escape clause

IBM® Engineering Requirements Quality Assistant (RQA) message: This requirement includes a phrase such as when possible, if necessary, or as required that makes the requirement unclear and difficult to verify. Effective requirements use specific wording that can be interpreted only one way. Eliminate or replace phrases that are unclear or provide loopholes.

Explanation

Phrases with conditions that allow requirements to not be met are considered escape clauses because you can evade fulfilling the requirement under those conditions. For example, phrases such as, as much as possible or if practical mean that the requirement does not need to be met all the time. Escape clauses make requirements vague and difficult to verify

Example

Consider the following requirement:

The system shall have a login console for company employees to log in remotely, where possible.

If a contractor who implements the system sees the where possible phrase, the contractor might decide to provide a console for employees who log in remotely from company sites. The contractor might exclude non-company sites, such as employees’ homes. Logging in from a non-company site requires the contractor to implement additional security measures, which affect the cost and time of the implementation. For a company in which employees travel frequently or work from home, logging in from non-company sites is essential.

The problem lies in the interpretation of where possible. To the contractor, where possible means if it can be implemented within the current budget, but to the requirement author, where possible means where technically possible, regardless of cost.

To avoid confusion, be specific and eliminate the phrase where possible:

The system shall have a login console for company employees to log in remotely.
The system shall have a login console for company employees to log in remotely over the internet.