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11.3.4 Component with behavior must have a trigger

Any component with a behavior specification is supposed to be ’reactive’. This implies that it should have at least one provides interface with an in-event, or at least one requires Interface with an out-event. Such an event acts as a trigger for the component to react on. So-called “active” components are not supported.

An example: 

interface iworld
{
  out void world ();
  behavior {on optional:world;}
}

component component_provides_without_trigger
{
  provides iworld p;
  behavior {}
}

This results in the following error message: 

component-provides-without-trigger.dzn:7:1: error: component with
    behavior must have a trigger

Another example: 

interface ihello
{
  in void hello ();
  behavior {on hello:{}}
}

component component_requires_without_trigger
{
  requires ihello r;
  behavior {}
}

This results in the following error messages: 

component-requires-without-trigger.dzn:7:1: error: component with
    behavior must define a provides port
component-requires-without-trigger.dzn:7:1: error: component with
    behavior must have a trigger