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Embedded Systems December 2000 Vol13_13

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e more important, how to link these two things together. There's much more to ROPE . For example, we didn' t touch on how design patterns are applied, the impor- tance of executable models in elIective- Iy constructing spiral models, how to tum requirements scenario into te L vectors, or how to estimate cost and time for the spi rals and prototypes. The ROPES process is highly scaleable. It's sui table for single-person proj ects all tJle way th rough proj ects with hundreds of develope rs. Scaleabili L)' is largely done Lhrough selecting which artifacts need to be gen- erated . In a small proj ect, communica- tion witJl a small team may require only a few artifacts and less detail , because the L eam members are all co-located and the system is simple. For large sys- tems, more ritual and detail is necessary because there will be more diversity in the team members, the cost of failure is higher (relative L o tJle co t of producing the artifacts), the teams may not be co- located and the system is very complex. In such systems, more rigor is required to ensure that tJle much larger n um ber of requirements are properly rendered in the analysis and design, and LO com- municate the exponentially greater number of details that ari e in a large complex system. The ROPES process has evolved out of my experience in constructing many differe nt kinds of systems over the last 20-odd years. Ideas that didn 't work well were discarded, and successful ideas were more strongly supported . Currently, ROPES is a well-understood and successful approach to building systems of varying complexities. It is being used successfully on many pro- j ects. It can help yours too. esp 13'ru.ce Powel Douglass has 20 years of experience designing sapty-critical real- time aptJlications in a variety of haTd rea l-time enviTOnments. He has designed and taught courses in object oTien tation, recti time, and safety-criti- cal systems develojnnent. He is the autho' r of several books including Real- Time UML: Effi cie nt Objects for Embedded Sys tems (Addison-Wpslry, 1998) and Do ing Ha rd Time : Deve loping Real-Time Sys tems with UML, Objects, Framewo rks, and Patte rn s (A ddison-Wesley, 1999). He is currently emlJloyed as the Chief Evangl'lis t at f-Logix, and you can e- mail him at bfJd@ilogix.com. References 1 . Actors are objects outside the scope of the system that interact with the system. 2. Douglass, Bruce Powel. Doing Hard Time: Developing Real- r,me Systems with UML, Obiects, Frameworks, and Patterns. New York: Addison-Wesley, 1999. El11bedded Systel11s Progral11l11ing DECEMBER 2000 151

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