Software Engineering

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CHAPTER 8 
Software Requirements Analysis Practice
8.3.1 
Identify modes of operation
Most applications must be designed to operate in different modes that address nor-
mal, degraded, maintenance, and training modes. The operational model should be 
evaluated to identify alternative modes of operation to determine the specific con-
ditions that will transition the application from one mode of operation to another. 
For example, if an ATM banking machine runs out of cash to dispense, it cannot 
conduct withdrawal transactions, but it can still process other transaction requests. 
However, when the ATM machine is undergoing maintenance to replace wornout 
parts or to refill the cash, receipts, and other consumables, the ATM is taken out of 
service and no transactions can be conducted.
Separate operational models can be developed for each alternative mode of oper-
ation, or the operational model can account for each of the modes of operation. It is 
sometimes more efficient to initially separate the operational, training, and support 
models so that each model is given a defined focus. Once they are complete and 
verified, these models can be integrated or combined into a single model, if desired.