The Functional Breakdown is a structured breakdown of every function that the system must support. The functional breakdown is used to express the requirements of a system in order to accomplish a certain capability or mission. It may also be used for product management, integrating systems-of-systems (products) to achieve a certain capability (system-of-systems), and reliability engineering (c.f. the Fault DEX where the faults effects are described in terms of functional impact).

The business process for which the DEX provides information is summarized in the SysML activity diagram in Figure 1.