Rationale

State variables are supposed to represent the state of a model, which in turn is supposed to change due to the occurrence of events.
There are very few good reasons to have a simulator carry state variables that never change.

Symptoms

The trace does not contain any events where an action changes the value of this variable.

Diagnosis

• The state variable may be read-only and an artefact to encode an input parameter setting for a model. In this case, the variable is simply ok.
• Actions that are supposed to make changes may not occur because the trace is too short, their enabling conditions are too strict to be met by any means, or there are other competing actions that the simulator prefers (may be due to a random switch, due to timing or due to priority settings among actions).
• Actions that are supposed to make changes do occur but fail to make appropriate assignments to this variable.

Verification and Therapy

• Check the model specification on what actions are supposed to make changes to this state variable.
• If there are none, then why does the variable exist (if it is not for representing an input parameter)?
• If actions exists, check if those actions in deed occur. You can look for warnings of type 5 in this report or use the event browser in Traviando.
• If corresponding actions do not occur, then this might be because the trace is too short or because they cannot be enabled. Check for the occurrence of actions that should enable those actions that would make changes to the variable. If those actions occur, check what competing actions the simulator executes and why.
• If corresponding actions do occur, check the state transformation they perform, either in the Traviando report or in Traviando' s message sequence chart which allows you to locate an event and see state descriptors before and after the event. Check the observed state transformation for being consistent with the model specification.