<From Wikipedia>
RIF/ReqIF (Requirements Interchange Format) is an XML file format that can be used to exchange requirements, along with its associated metadata, between software tools from different vendors. The requirements exchange format also defines a workflow for transmitting the status of requirements between partners. Although developed in the automotive industry, ReqIF is suitable for lossless exchange of requirements in any industry.
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For the CAC, ReqIF is important because it allows for the exchange of requirements information between Comet / CDP4 and other requirements management systems such as IBM Rational Doors. By automating the exchange of requirements information it becomes possible to have Comet / CDP4 automatically validate that systems modeled in SysML are meeting the requirements specified in Doors.