Common Modeling Techniques
Modeling the Lifetime of an Object
To model the lifetime of an object:
- A class, a use case, or the system as a whole can be modeled as a state machine
- If the context is a class or a use case, find out the neighboring classes (which may include any parents of a class) and any classes that are accessible by associations or dependencies
- These neighbors are candidate targets for actions and hence, may figure in guard conditions
- Limit the focus to one behavior of the system, if the context is the system as a whole
- Including all objects is unpractical and counterproductive even if they participate
- Set up the initial and the final states of the object
- Provide the pre and the post conditions of the initial and the final states that determine the rest of the model
- Choose the events to which the object may respond
- If the events are already specified, they can be found in the object's interfaces. Otherwise, consider the objects may be dispatched by that a
- Identify the states the object may be in, from the initial to final state
- Associate these states using the transitions triggered by the appropriate events
- Add actions to these transitions
- Identify any entry or exit actions
- Expand these states by using substates wherever necessary
- Verify that all the events specified in the state machine match the events expected by the interface of the object and vice versa. Some events may be ignored
- Make sure that all actions mentioned in the state machine are supported by the relationships, methods, and operations of the enclosing object
- Trace through the state machine, either manually or by using the tools to check the state machine against expected sequences of events and their responses
- Carefully identify unreachable states and those states in which the machine may not respond
- Make sure that the object's semantics are preserved
