I. Introduction
The presense of alarm floods impairs the effectiveness of the alarm system. In an alarm flood, a large number of alarms are generated, with the result that the alarm system is partially or completely inoperative [1]. In the ANSI/ISA-18.2 standard [2], an alarm flood is known as a situation that the amount of alarms exceeds the management capability of an operator. Therefore, it is crucial to identify and address the root cause of alarm floods as soon as possible. The alarm flood sequences are usually analyzed to solve this problem. This is because alarm flood sequences generally have some degree of recurrence and similar floods usually suggest that they have the same root cause. In the past decade, many sequence alignment methods have been proposed to compare alarm flood sequences; the results are helpful for root cause analysis and online prediction.