Alex, our expert Systems Engineer, continues to help us fully understand use cases and their purpose with his latest blog post... Identifying the primary actors has allowed us to validate the context of the system however it is the goals of the primary actors that we are really looking for as they will help us discover our use cases.
An actor goal represents a service that the primary actor requires from the system.
A use case is always started by an actor and so focussing on the actors yields good results.
In addition, there may be external events that we must react to such as start-up, shut-down and time related events that we might not have considered given our set of actors. When identifying actor goals we should consider:
- What are the tasks of an actor?
- Does the actor need to be informed about certain occurrences in the system?
- Are there any external events that affect the system? What actor informs the system about those events?
- How the system starts-up and shuts down
- How the system is maintained?
- How will we handle training users of the system?
- Does the system store information? What actors will create, read, update or destroy that information?
A table is often created during this phase and is frequently referred to as an actor goal list. If a large number of primary actors have been created then this table is likely to be quite extensive. This is not overly significant as the worst that is likely happen is that we will generate the same goal more than once. Once the actor goal list has been generated, the list must be reviewed and rationalised.
The rationalised actor goal list provides an initial list of use cases that must now be documented.
It is likely that you will not find all the goals during this stage, no matter how careful or diligent you are. New ones will appear when documenting the use cases.
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