In the previous chapter, we showed how approaches to dependability have
changed over the years, and went on to defi ne Open System Dependability
(OSD) as a new dependability concept and discuss the basic methods for
making this concept a reality. In order to satisfy the requirements of OSD, a
system must possess functionality for accommodating changes in its objectives
and its environment, functionality that facilitates continuous operation, and
functionality for ensuring that accountability with regard to the system can
be consistently achieved; in addition, this functionality must be integrated
into the system itself in the form of a repetitive process. The dependability of
the system can thus be improved in iterative steps. In this chapter, we will lay
out the structure of the specifi c technologies required to realize OSD as the
Dependability Engineering for Open Systems (DEOS) Technological System.
We have shown that the achievement of OSD requires functionality for
accommodating changes in the objectives and environment of the system. This
change accommodation functionality relates to system changes that occur both
during development and after the start of operation, and it is closely tied to
the process of system development. We have also shown that, in order for the
system to deliver the expected services to users as continuously and safely
as possible, it must have both failure prevention functionality and responsive
action functionality. These preventive action and failure response functions are
linked to the process of system operation. Whenever the failure preventive and
responsive action functionality have been utilized, changes must be made to
the system in order to realize recurrence prevention. That functionality initiates
system development from the system operation stage.
To ensure that accountability can be consistently achieved, analysis of the
causes of a failure (cause analysis) must be performed promptly. To do this, the
system needs (1) agreement log retention functionality for structured description

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