With the growingubiquity of computing systems it is essentialthat we canplace reliance on the services they deliver. This is particularly obvious and important in areas like aircraft avionics, global ?nancial transaction processing, or nuclear power plant control where human lives or large ?nancial values are at stake. But also the worldwide daily nuisances of computer viruses or data corruptions caused by crashing operating systems collectively impose high costs on society, which are beginning to become economically relevant. Within computer science, the termdependability has been introduced...