On Local Certifiability of Software Components

Large software systems, like other large engineered systems, consist of components that are meant to be independent except at their interfaces. An important aspect of any large system is the need for local certifiability: to be able to establish properties of components out of the context of the larger system(s) in which they are embedded, and to be sure that any properties thus certified are certain to hold even when the components are composed with others to build larger ones. This is especially important for "black-box" reusable components, which need to be prequalified for inclusion in a component library. A good software engineering discipline must support local certifiability of important component properties, or life-cycle costs are inherently doomed to spiral out of control for larger and larger systems. No software engineering discipline in general use today can support local certifiability of most interesting properties. But local certifiability of many important properties — including, crucially, correctness with respect to an abstract specification — is possible in at least one practical discipline (Hollingsworth 92b).