A transition signifies when an object moves from one state to another state when a specified event occurs, provided that certain specified conditions are satisfied. When such a change of state occurs, the transition is said to 'fire'.
A transition is represented by a vector that contains the name of the event causing the transition. A transition can contain an event, an event and a condition, or no event at all.
A transition that contains an event and a condition is called a conditional or guarded transition.
Trigger event
The Trigger Event is the name of the event that causes the transition to 'fire', provided the guard condition is satisfied. When you add a Trigger Event name, the Transition name is hidden and the Trigger Event name is shown its place. The Trigger Event name acts as the Transition name. If you do not add a Trigger Event, the symbol displays the Transition name.
However, you can customize System Architect to display the Trigger Event name and the Transition name simultaneously. This customization only affects the System Architect sessions of users who apply it. Each user who wants the functionality needs to apply the customization.
To display the Trigger Event name and the Transition name
1 Open the sa2001.ini file, located in C:\Documents and Settings\<UsernName>\Local Settings\Application Data\Telelogic\System Architect by default.
2 Find the [SystemArchitect] section, and add IgnoreAlternateNameRule=Y underneath it as shown below:
[SystemArchitect] IgnoreAlternateNameRule=Y
3 Save and close the sa2001.ini file.
4 Restart System Architect. The Transition name and the Trigger Event name are both now displayed on the diagram. Optionally, you can still hide the Transition name if you want to display only the Trigger Event name, as follows:
▪Right-click the Transition symbol, and then click Display Mode.
▪Select Hide Symbol Name, and then click OK.
Parameters
The triggering event may have parameters. Within the Parameters field, you may list these parameters by a comma-separated string.
Guard condition
You may optionally specify a guard condition for the transition to 'fire'. The guard condition is evaluated when the transition is triggered by the trigger event. If the condition expression is true, the transition is eligible to “fire”. If it is false, the transition does not fire and if there is no other transition that could be triggered by that same event, the event is lost. The guard condition is an expression written in terms of parameters of the triggering event and attributes and links of the element that is being modeled by the state diagram.
Effect (action)
The effect of the transition, besides causing a change of state, may be to cause an action to be performed. The action specified on a transition line is executed when the transition “fires”. It may be written in terms of operations, attributes, and links of the owning object and the parameters of the triggering event. The action must be executed entirely before any other actions are considered.
Send Event
The effect of the transition may be to send an event. You may list the name of the event within the Send Event property.
