As shown in Venn diagram (Figure 5), three types of NFRS: performance, security, and usability are NFRS that are considered in all five types of systems, while reliability is a type of NFRS considered in four types of syslems (real-time systems, safety- critical systems, information systems, and process-controlled systems). It indicates that the former three NFRS are the most common NFRS in each type of software being developed.