Design for X (DfX) is a term used to describe a series of design guidelines, such as Design for Manufacturing, Design for Six Sigma, Design to Cost, and Design for Test. ^[10] For example, Design for Test can include inserting probe points on a circuit board. Each of these captures downstream constraints or considerations and propagates them back upstream. Having covered implementation and operations broadly, let’s see what other considerations have been captured under Design for X.

One way to think about the universe of Design for X is in terms of the following list of “ilities,” or attributes of the system that are related to its implementation and operations. The list of 15 “ilities” shown in Figure 10.5 was compiled over time by tracking mentions in journal articles; note the log scale on the vertical axis. Each of these attributes could act as a downstream influence.

However, not all “ilities” are architecturally distinguishing, and no one “ility” is always architecturally distinguishing. Although reliability may help distinguish between potential architectures for a pump, it may not distinguish between vehicle architectures if the architectural decisions don’t define the attributes that relate to reliability; these attribute may arise only from detailed design decisions or choice of assembly method. Maintainability may be a function of whether a tablet’s architecture has an integral case design or a modular case design, but it may also be a function of an individual component that has no bearing on the architecture, such as how easy it is to clean the screen as a function of the coating on the glass.

It is also worth noting that the “ilities” are not independent. For example, the durability of the architecture may be correlated with the emphasis placed on quality in manufacturing, the modularity of the architecture may impact the adaptability of the architecture, and the robustness of the architecture could be inversely proportional to its flexibility.