The id of the activity template related to the current event 与当前事件关联的活动模板的id 。
2.
Two events belong to the same activity instance if they have the same activity template id atid and the same process instance id piid 如果两个事件具有相同的活动模板id ( atid )和相同的流程实例id ( piid ) ,那么这两个事件就属于同一个活动实例。