There are no events in the links between action states. The start state is a pseudo-state. There may be an event in the link between it and the first action state. There may be guards, send-clauses and action expressions attached to the links. When no link label is present, as soon as the ``from'' action state finishes the ``to'' action state starts. Guard conditions on the links may stop this happening. Decisions (``diamond-shaped'' symbol) are controlled by guards.