A rule expresses a programmatic response to a set of conditions. A rule contains a text and a set of attributes. When a rule fires, it executes one or more actions. For information about actions, see Chapter 19, Actions.
if the level of any tank = 0
then conclude that the status of the tank is empty
if: Invocable in many ways
initially: Responds to the activation of its parent workspace
unconditionally: Executes its actions each time it is invoked
when: Like if rules, but cannot participate in chaining
whenever: Responds to events
for prefix in the text of the rule.
You can use G2's facilities for debugging and tracing to monitor the execution of rules. These facilities notify you when a particular rule has been invoked, suspended, and completed. You can also direct G2 to highlight the text box representation of each rule as it is invoked.