An information flow model of fault detection

RELAY is a model of how a fault causes a failure on execution of some test datum. This process begins with introduction of an original state potential failure at a fault location and continues as the potential failure(s) transfers to output. Here we describe the second stage of this process, transfer of an incorrect intermediate state from a faulty statement to output. Transfer occurs along information flow chains, where each link in the chain involves data dependence transfer and/or control dependence transfer. RELAY models concurrent transfer along multiple information flow chains with transfer sets, which identify possible interaction between potential failures, and with transfer routes, which identify actual interactions. Transfer sets, transfer routes, and control dependence transfer are unique to the RELAY model. The model demonstrates that the process of potential failure transfer is extremely complex and full analysis of real programs may not be practical. Nonetheless, RELAY provides insight into testing and fault detection and suggests an approach to fault-based testing and analysis that may be warranted for critical systems software.