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184 S o f t w a r e & S y s t e m s R e q u i r e m e n t s E n g i n e e r i n g : I n P r a c t i c e

[Perf-PLATFORM-1] [Perf-PLATFORM-2]

[Perf-COMP1-1] [Perf-COMP1-2] [Perf-COMP2-1]

FIGURE 6.2 Example platform-level NFR model

The platform-level NFR model captures how the platform-level
NFRs are refined into the components and their relations. The major
relation is “support” that shows which component-level NFRs
support which platform-level NFRs. For an example, see Figure 6.2.
The component-level NFR model shows the relations among the
NFRs at the component level. The major relations are “reference,”
“replace,” and “deprecated” (a self-relation). It also shows what
platform-level NFRs they support as well. The reference relation
indicates that one NFR is built upon another NFR. For example, one
performance requirement might be that a rate should be two times
faster than the rate defined by another NFR. The replace relation
shows one NFR has been replaced by another NFR. One NFR could
also be replaced by more than one NFR, as shown in Figure 6.3.
Check for Consistency
This activity checks the consistency between the NFRs at the platform
level with those at the component level. The NFRs at the platform

[Perf-PLATFORM-1] [Perf-PLATFORM-2]

[Perf-COMP1-1] [Perf-COMP1-2] [Perf-COMP2-1]

Replace

[Perf-COMP-1-3] Replace

FIGURE 6.3 One NFR [Perf-COMP-1-3] replaced by two NFRs, [Perf-COMP1-2]
and [Perf-COMP2-1]