measuring reliability as a mean failure cost.pdf

Measuring Reliability as a Mean Failure Cost Ali Mili, CCS, NJIT Newark NJ 07102-1982 ******@ Frederick Sheldon, ORNL, 1 Bethel Road Oak Ridge TN 37831 ******@ The Mean Time to Failure (MTTF) is monly ac- cepted measure for system reliability. Some variations of it (MTTD: mean time to detection of a vulnerability, and MTTE: mean time to exploitation of vulnerability) have also been adopted to measure other dependability at- tributes [2] (most notably security). In this fast abstract we submit a tentative challenge to this measure, propose an alternative, and brie?y illustrate it with a simple example. When we say that a system has an MTTF , we mean that the mean time to the failure of the system with respect to some implicit speci?cation is . In doing so, we are usually making three implicit assumptions: Independence of failure cost with respect to subspec- i?cations . plex speci?cation is typically the aggregate of many individual requirements/ subspec- i?cation; the stakes attached to meeting each require- ment vary from one requirement to another. Yet the MTTF makes no distinction between requirements; failing any requirement counts as a failure. Independence with respect to stakeholders . Typically the operation of a system involves many stakeholders, who have different stakes in the system meeting any given requirement. Yet the MTTFis not dependen