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3. Activity diagrams.
In the early stages of requirements analysis, the aim is to identify
the various actors and use cases, and to understand in perhaps some
general sense how these ingredients are related. However, at some point,
it becomes important to gain a more complete understanding of how
the system will behave in an operational sense. This means describing
the system in detail "from the outside" without regard to what is taking
place internally to effect this behavior. Ideally, this should be decided
before making important design decisions. This external behavior is likely
to be too intricate to be successfully capture in words and use case diagrams.
Here activity diagrams can be quite
helpful. This sort of diagram is a descendant of the traditional "flow chart"
and is good for represent intricate sequencings of system activities.
As an example, the following diagram specifies how the jukebox's selection
process should proceed.
Figure II.3
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