Defining changeability: Reconciling flexibility, adaptability, scalability, modifiability, and robustness for maintaining system lifecycle value

Abstract

Designing and maintaining systems in a dynamic contemporary environment requires a rethinking of how systems provide value to stakeholders over time. Developing either changeable or classically robust systems are approaches to promoting value sustainment. But, ambiguity in definitions across system domains has resulted in an inability to specify, design, and verify to ilities that promote value sustainment. In order to develop domain-neutral constructs for improved system design, the definitions of flexibility, adaptability, scalability, modifiability, and robustness are shown to relate to the core concept of "changeability," described by three aspects: change agents, change effects, and change mechanisms. In terms of system form or function parameter changes, flexibility and adaptability reflect the location of the change agent-system boundary external or internal respectively. Scalability, modifiability, and robustness relate to change effects, which are quantified differences in system parameters before and after a change has occurred. The extent of changeability is determined using a tradespace network formulation, counting the number of possible and decision maker acceptable change mechanisms available to a system, quantified as the filtered outdegree. Designing changeable systems allows for the possibility of maintaining value delivery over a system lifecycle, in spite of changes in contexts, thereby achieving value robustness.

Climate adaptive building shells: State-of-the-art and future challenges

“…More intuitively: flexible systems make transitions over time [45], to meet new circumstances and cope with uncertainty, and thus imply an ease of modification and absence of irreversible or rigid components [46]. Whereas robust designs try to neutralize the impacts of external perturbations, flexible designs do the opposite by intentionally exploiting the changes in their environment.…”

Value-driven product service systems development: Methods and industrial applications

“…Other dimensions pay a role in this respect, such as the scalability of the offer, etc. These notions are well known within the VDD community, where methods and tools for the analysis of so called "ilities" (which are Flexibility, Adaptability, Scalability, Modifiability, and Robustness) for maintaining system lifecycle value have been proposed since almost a decade (see: Ross et al 2008). Tradespace parameterization of systems can be exploited in this respect to design PSS solutions that are robust.…”

A simulation-based method to evaluate the impact of product architecture on product evolvability

“…The concept of ''product evolvability'' differentiate itself from the definitions of general design changeability (Fricke and Schulz 2005;Ross et al 2008) and design flexibility (Rajan et al 2005;de Neufville and Scholtes 2011;Tilstra et al 2013) by emphasizing heritance, path dependences and fitness-improving selection from an evolutionary perspective. Traditional engineering design change literature concerns changes in general, not differentiating positive (i.e., performance-improving) and negative (i.e., performance-reducing) changes.…”