The importance of the requirements definition stage in developing Ada for simulator systems is one of the "lessons learned" on the Ada Simulator Validation Program (ASVP). The traditional approach to requirements definition generally utilized for training systems is reviewed and some of the problems that result are discussed. The types of requirements that impact the design and life cycle support of the system are defined because of their significance to the process utilized for developing the system design. The impact that Ada and Object-Oriented Design implementations have on the requirements definition process is examined by first addressing the characteristics and features of Ada that satisfy software engineering concepts. Next, the decomposition and design procedures of the method and the manner in which requirements are utilized, for generating the software design are discussed. The process involved in the establishment of these requirements is also discussed. Finally, activities related to the systems requirements review process are addressed.