SimpleClassDiagrams Environment_PW{
    SimpleAttribute Integer{
        constraint = $
            String function constraint(model : Element, name : String):
                if (is_physical_int(model["model"][name])):
                    return "OK"!
                else:
                    return "Integer has non-integer value"!
    }

    SimpleAttribute Natural{
        constraint = $
            String function constraint(model : Element, name : String):
                if (is_physical_int(model["model"][name])):
                    if (integer_gte(model["model"][name], 0)):
                        return "OK"!
                    else:
                        return "Natural has negative value"!
                else:
                    return "Natural has non-integer value"!
    }

    SimpleAttribute String{
        constraint = $
            String function constraint(model : Element, name : String):
                if (is_physical_string(model["model"][name])):
                    return "OK"!
                else:
                    return "String has non-string value"!
            $
    }

    Class Named {
        name : String
    }

    Class Positionable {
        x : Integer
        y : Integer
    }

    Class Port : Named, Positionable {}
    Class Boundary : Named, Positionable {}
    Class Activity : Named, Positionable {}
    Class CommunicationSequence : Activity {}
    Class TopActivity : Activity {}
    Class Parallel : TopActivity {}
    Class Sequence : TopActivity {}
    Class Alternative : TopActivity {}
    Class Input : Event {}
    Class Output : Event {
        duration : Natural
    }

    Association Has1 (Boundary, TopActivity) {}
    Association Has2 (Boundary, Event) {}
    Association Has3 (Boundary, Port) {}
    Association HasActivity (TopActivity, Activity) {}
    Association HasEventSequence (CommunicationSequence, Event) {}
    Association NextEvent (Event, Event) {}
    Association PortEvent (Port, Event) {}
}