Software Engineering

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CHAPTER 12 
Configuring the Physical Architecture
Fault prevention involves establishing mechanisms intended to prevent faulty 
inputs or conditions from occurring. Fault prevention directly affects the design of 
the structural solution to ensure that all data introduced into a data processing trans-
action is within the acceptable, anticipated boundary for the data definition. This 
includes ensuring that all data entry and user interface interactions are supervised to 
prevent the introduction of improper data values.
Fault tolerance involves the detection of a faulty condition and selects a recov-
ery course of action. The fault recovery approach may return the software state 
to a previously saved state (backward recovery). Another fault recovery approach 
involves multiple functionally equivalent processes in a primary backup scheme 
where results are compared and the preferred result is selected with which to pro-
ceed (forward recovery). If three or more redundant processes are involved, then 
the comparison of intermediate results (voting) can determine which result is most 
likely incorrect and the dominant result can be selected to proceed with the data 
processing transaction (masking the incorrect result).
During software design synthesis it is important to address the need for fault 
detection and recovery in the specification of the structural solution. Fault preven-
tion will affect the individual specifications of structural units. Fault tolerance will 
impact the structural design solution to a greater extent to accommodate redundant, 
parallel data processing operations. Fault tolerance is a common engineering design 
concept for hardware products with redundant components working in parallel to 
ensure continued operational performance should one component fail.