“…Intermittent faults occur in software systems as well; consider for instance exceptions and interrupts that are caused by some unknown``bugs'' and that lead to crashes and reboots. The methodologies used in Aghasaryan et al (1998), Benveniste et al (2003), Bouloutas (1990), Console (2000), Debouk et al (2000), , , Lafortune et al (2001), Lamperti and Zanella (1999), Lin (1994), Lin et al (1993), Lunze (2000), Pandalai and Holloway (2000), Pencole  (2000), Pencole  et al (2001), Sampath (2001), Sampath et al (1998Sampath et al ( , 1995Sampath et al ( , 1996, Sengupta (2001), Sinnamohideen (2001), Westerman et al (1998) andHastrudi Zad et al (1998) assume that once faults occur, they remain in effect permanently; hence, the terminology``failures'' is often used for these permanent faults. Furthermore, to the best of our knowledge, diagnostic methodologies developed in the ®eld of model-based reasoning in arti®cial intelligence (which are close in spirit to the discrete event systems methodologies, since they are also based on qualitative system models) are also geared towards the diagnosis of permanent faults; see, for example, Darwiche and Provan (1996), Dvorak and Kuipers (1992), Chen (1998, 1999), and Williams and Nayak (1996).…”