Checklist for design, requirements specification and implementation

General Principles of Unexpected Events

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User Awareness

The reason for a system being built is primarily to replace manual work and make life more efficient. This means a system must be

• predictable

• handle events gracefully

• tell users exactly what is going on and what is expected

• report successful outcomes

• report unsuccessful outcomes with reasons

• report uncontrolled errors in a graceful manner

Handling Unexpected Events

Unexpected events must be dealt with properly. This means that

• every error which could happen is accounted for as far as possible

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• any error which occurs which

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• has not been controlled can be shown to the user

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• in a controlled way

Error Trapping

Error trapping has to be taken seriously for the smooth-running and predictable behaviour of an application. This means that anything Anything which is done as part of a calculation where user-supplied values are involved, has to have the information validated properly and any unexpected calculation results relayed to the user.

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• Product size field must be validated to make sure it has three values, separated by “x”

  • If the values are not separated by “x” then the product dimensions cannot be shown, but any screen or document should still be produced without them.

• A failure in the product size validation should not cause a failure in the whole system

Error Categorisation

What should stop an email being sent?

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