Defining System Changeability: Reconciling Flexibility, Adaptability, Scalability, and Robustness for Maintaining System Lifecycle Value

Designing and maintaining systems in a dynamic contemporary environment requires a rethinking of how systems provide value to stakeholders over time. Classically, two different approaches to promoting value sustainment may include developing either alterable or robust systems. The first accomplishes value delivery through altering the system to meet new needs, while the second accomplishes value delivery through maintaining a system to meet needs in spite of changes. The definitions of flexibility, adaptability, scalability, and robustness are shown to be different parts of the core concept of “changeability,” which can be described by three aspects: change agents, change effects, and change mechanisms. Cast in terms of system parameter changes, flexibility and adaptability are shown to relate to the origin of the change agent (external or internal to a system boundary respectively). Scalability and robustness, along with the additional property of modifiability, are shown to relate to change effects. The extent of changeability is determined by the number of possible change mechanisms available to the system as accepted by decision makers. Creating changeable systems, which can incorporate both classical notions of alterability and robustness, empowers systems to maintain value delivery over their lifecycle, in spite of changes in their contexts, thereby achieving value robustness to stakeholders over time.