Abstract: Safety requirements have commanded increasing attention as software is playing a more and more important role in today’s safety critical systems.The extraction and description of software safety requirement are the key element of the whole software safety work.The subsequent software design and realization and test process will reference to software safety requirement.Nevertheless,most safety requirements are described in ordinary functional specification,lack of independent and normative description,especially the relationship between safety requirements and fault,failure.As a result,there is little practical guidance on how to describe safety requirements.So this paper designed a safety requirements specification－Safety RUCM,which is based on restricted use case modeling RUCM,and extended its specification template and restriction rules by adding fault specification and data specification in order to support the fault related information.We used this specification to describe an operating system safety requirement.Result shows that this specification is practicable.

Key words: Safety requirements,Restricted use case modeling,Data dictionary,Fault