Software Engineering

11.2.7 
Identify failure conditions
Every functional transaction must be evaluated to identify situations or conditions 
that may cause failure conditions. Identified failure states must be resolved by stip-
ulating the data integrity criterion that must be interrogated to determine a failure 
state, and the actions to be taken when a certain state arises to complete the data 
processing transaction.

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11.2 
Behavioral analysis
Some failure conditions may result in a state that cannot be resolved via auto-
mation and requires human intervention. The functional analysis effort must then 
address the manner by which the software will continue to operate in a degraded 
mode, if possible. For example, if an ATM’s supply of money has been depleted, 
then the withdrawal function must be temporarily suspended until the money supply 
if restocked. The software functions for detecting failure conditions and operating in 
a degraded mode must be included within the functional architecture. This includes 
identifying how the software product can be “informed” of the current state of data 
processing or system resources and how the state indicators are managed.
Potential data processing failure modes and effects must be analyzed to deter-
mine how the software product should behave in response to each failure condi-
tion. Failure modes and effects analysis (FMEA) is an engineering procedure that 
enables the design team to classify potential failure modes by the severity (con-
sequences) and likelihood of the failures resulting with improved product quality 
and dependability. 
Dependability
 is a term that is better suited for software prod-
ucts than reliability. Throughout the engineering community, reliability deals with 
predicting the mean time between failure (MTBF) of hardware components during 
normal operation and provides an estimate of the expected duration life expectancy 
for the component. Software does not breakdown or wear out over time with use. 
Therefore, dependability refers to a software component’s ability to perform its 
function as expected under all circumstances. Dependability is a more suitable term 
to be used for software products due to the nature of the material of which it is 
comprised. If a software component fails, it is due to the software design inability 
to be resilient to unexpected circumstances or situations.
Software FMEA should be used to identify potential failure modes, determine 
their effects on the operation of the system or business process, and design response 
mechanisms that prevent the failure from occurring or mitigate the impact of the 
failure on operational performance. While anticipating every failure mode may not 
be possible, the development team should formulate an extensive list of potential 
failure modes in the following manner: