Exceptions and Alternatives


Chapter 6 introduced the idea of exception cases for a product use case. Exceptions are unwanted but inevitable deviations away from the normal case caused by errors and incorrect actions. The exception scenario demonstrates how the product recovers from the unwanted happening. The procedure for writing the requirements remains the same: Go through each of the exception steps and determine what the product must do to accomplish that step.

For these requirements, you must make it clear that they become reality only if the exception exists. To do so, you might identify a block of requirements as being attached to a particular exception or write each one to include the exception condition:

If there are no trucks available, the product shall generate an emergency request to truck depots in adjacent counties.


Alternatives are allowable variations from the normal case, which are usually provided at the behest of the business stakeholders. A well-known example is Amazon's 1-Click product. If you have already used a credit card with Amazon, you have an alternative path available to you when buying goods: Instead of going through the normal check-out routine, the goods are recorded as sold as soon as you click on them. The normal case would look like this:

The product shall add the selected item to the shopping cart.


Here is the alternative:

If 1-Click is turned on, the product shall record the sale of the selected item.


Be prepared to create many requirements to handle the exceptions and alternatives. Indeed, these sometimes make up the bulk of the requirements. Given that, as human users of software systems, we are capable of the most bizarre actions, you will need to specify a great deal of recovery functionality.




Mastering the Requirements Process
Mastering the Requirements Process (2nd Edition)
ISBN: 0321419499
EAN: 2147483647
Year: 2006
Pages: 371

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