What is the preferred type of identifier for requirements that should not be altered or reused?

A unique numeric identifier is a robust choice for requirements that should remain unchanged and not be reused. This type of identifier ensures each requirement has a distinct and unambiguous reference, making it easy to track and manage throughout the project lifecycle. Because it is numeric, it is less prone to errors associated with textual identifiers, such as typographical mistakes or variations in wording.

In the context of requirements management, using a unique numeric identifier helps maintain the integrity of the requirement throughout its life cycle, from initial documentation through its implementation and verification. Once a requirement is assigned a unique numeric identifier, it serves as a permanent reference that stakeholders can reliably use to refer back to that exact requirement, facilitating clarity and consistency in communication around that requirement.

Other types of identifiers may not offer the same level of permanency or uniqueness. For example, a textual identifier can become ambiguous as the documentation evolves. An absolute reference typically points to a specific location or context, which may not be stable over time, and a temporary reference implies that the identifier is only valid for a limited duration, which does not align with the need for a lasting and reliable reference for unaltered requirements.