Software Component Dependability, a Subdomain-based Theory

A prole-dependent \dependability " for software can be dened using a functional prole (a set of input-space subdomains breaking down the behavior of a component according to its specication { these are the subdomains used in the usual \functional testing"). It is argued that measurements of dependability using the squeeze play (1) are prole dependent in general; but, (2) when the prole is dened by weighted subdomains, the squeeze-play predictions depend only on the subdomains, not on their weighting, hence this dependability is prole independent. A component developer can de ne functional subdomains for the component and measure the dependability, then market the component with its dependability description. A system developer could select components with attached dependabilities, combine the components in a veried structure, and measure { from the component dependabilities alone { a system dependability. However, the system dependability is not prole independent. Measurements for both component- and system developer can be supported by tools