Fault tree construction of hybrid system requirements using qualitative formal method

Jang Soo Lee, Sung Deok Cha

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


When specifying requirements for software controlling hybrid systems and conducting safety analysis, engineers experience that requirements are often known only in qualitative terms and that existing fault tree analysis techniques provide little guidance on formulating and evaluating potential failure modes. In this paper, we propose Causal Requirements Safety Analysis (CRSA) as a technique to qualitatively evaluate causal relationship between software faults and physical hazards. This technique, extending qualitative formal method process and utilizing information captured in the state trajectory, provides specific guidelines on how to identify failure modes and relationship among them. Using a simplified electrical power system as an example, we describe step-by-step procedures of conducting CRSA. Our experience of applying CRSA to perform fault tree analysis on requirements for the Wolsong nuclear power plant shutdown system indicates that CRSA is an effective technique in assisting safety engineers.

Original languageEnglish
Pages (from-to)121-131
Number of pages11
JournalReliability Engineering and System Safety
Issue number1
Publication statusPublished - 2005 Jan
Externally publishedYes

Bibliographical note

Funding Information:
The work described here was supported in part by the Ministry of Science and Technology under the KNICS project, and in part by AITrc of KAIST.


  • Fault tree
  • Formal method
  • Hybrid system
  • Requirements
  • Software safety

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Industrial and Manufacturing Engineering


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