RELIABILITY SPECIFICATION:
The process of reliability specification can be based on the general risk-driven specification process.
1. Risk identification: At this stage, you identify the types of system failures that may lead to economic losses of some kind. For example, an e-commerce system may be unavailable so that customers cannot place orders, or a failure that corrupts data may require time to restore the system database from backup and re-run transactions that have been processed.
2. Risk analysis: This involves estimating the costs and consequences of different types of software failure and selecting high-consequence failures for further analysis.
3. Risk decomposition: At this stage, you do a root cause analysis of serious and probable system failures. However, this may be impossible at the requirements stage as the root causes may depend on system design decisions. You may have to return to this activity during design and development.
4. Risk reduction: At this stage, you should generate quantitative reliability specifications that set out the acceptable probabilities of the different types of failures. These should, of course, take into account the costs of failures. You may use different probabilities for different system services. You may also generate functional reliability requirements. Again, this may have to wait until system design decisions have been made. It is sometimes difficult to create quantitative specifications. You may only be able to identify functional reliability requirements.
