Conclusions

Abstract

Software systems have become so much an integral part in our lives that we now naturally interact with them on a daily basis. We buy merchandise using the worldwideweb, and obtain cash from automatic teller machines. We hardly use actual money any more; when we need to make a purchase, the sums of money are usually being transferred as data communication between distributed computer systems. Computers control traffic light systems, aircraft navigation and complicated medical equipment. We trust these systems to work properly. A computer printout is often brought as evidence to support some argument in a discussion or a dispute. We expect that for critical systems, the likelihood of making an error is smaller than the chance of a human operator making the same mistake.