Embedded Systems December 2000 Vol13_13

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The semi-spirallifecycle gets its name from the fact that the requirements analysis and systems engineering are not part of a large overall spiral. FIGURE 1 r~l :1)- 1 = , = ' ················: l§ Process : guidelines : and standards : • .. : Work gUidelines : and standards ••• .. Schedule ~ r··· j~ L~ t Results in ~~------~--, Creates, manages, or uses . r .................. ~ 1UfffiC£ ••••••••••• • ----- === ............ : 1= 1= 1= • i=== ~ ~ • Template • Rev of process steps within a phase of the microcycle. Typically 30 minutes to 1 day. 142 DECEMBER 2000 Embedded Systems Programming =I~- ra'1=== - 1=== Guideline Defect Report the ROPES process provides an alter- native lifecycle, called the semi-spiral lifecycle, which is shown in Figure 3. The semi-spiral lifecycle gets its Configuration Management System name from the fact that the require- ments analysis and systems engineer- ing are not part of a large overall spi- raJ. Internally, they do operate in a spi- ral fash ion, but once they deliver their artifacts, they are not revisited. However, the engineering aspects against the requirements and subsys- tem model do proceed in a spiral fash- ion, with the multidisciplinary subsys- tems being integrated together fre- quently. This alternative approach is often more palatable to organizations accustomed to waterfall approach for very large-scale systems. It provides some, but not all of the benefits of a true spiral development lifecycl e. The development and iteration of the design of the system does occur in the semi-spiral lifecycle, but it is not very resilient in the presence of unknown or changing requirements and great care must be taken to ensure that the high level systems engineering model is solid before allowing the subsystem teams to begin working. The spiral microcycle Figure 4 shows the standard ROPES microcycle. The primary phases of the spiral are shown in Table 1. The ROPES spiral is different from Single iteration resulting in a single prototype. Typically 4 to 6 weeks. most other spiral processes in a couple of ways. First, note the system engi- neering subphase in analysis. This sub- phase is not a lways required, but should be present for eitller complex software systems or when there is hard- ware-software codesign. Systems engi- neering identifies a high-level subsys- tem or component architecture and decomposes the system-level use cases to subsystem-level use cases that map to individual subsystems. These subsys- tems are then further decomposed into the various disciplines of software, electroni c, mechanical , and possibly even chemical engineering. The party phase is where initial project p lanning takes place, as well as

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