## Questionsexercises

8.1 Define two additional steps in the process of requirements analysis, in addition to the essential steps cited in this chapter.

8.2 Functionally decompose an automobile system. Define two requirements for each of the decomposed elements.

8.3 Identify and briefly describe two automated requirements analysis tools that are available from software vendors, other than those mentioned in this chapter.

8.4 Contrast the NASA perspective on handling requirements with the approach taken by the Department of Defense.

8.5 Verify the compatibility between the stated MTBFs and the failure rates in Figure 8.3. Given a system composed of four independent subsystems with MTBFs of 200, 250, 500, and 1000 hours, what is the MTBF of the overall system?

8.6 A system with three independent subsystems has a total failure rate of 0.0108. We also know that the MTBFs of the subsystems are in the ratio 2:3:4. What are the subsystem MTBFs and failure rates?

8.7 a. The total admissible error variance for a system is 70 and two of the three subsystem root-mean-square (rms) errors are 4 (value of x) and 6 (value of y). What is the largest acceptable integer value of the third error source (z) if all error random variables are additive and independent?

b. Recalculate your answer if the error model is based on the relationship: total error = 2x + y + z

8.8 Systems can be designed such that errors correspond to multiples of standard deviation (sigma) values. If the resultant distribution were normal (Gaussian), interpret numerically the intended consequences of designing to the one-sigma, two-sigma, and three-sigma values.

### REFERENCES

8.1 United States General Accounting Office (GAO) Report for the Acting Secretary of the Air Force, Defense Support Program, GAO/NSIAD-93-148 (1993). Washington, DC: USGAO.

8.2 Systems Engineering, Military Standard 499B (Draft) (1991). Washington, DC: U.S. Department of Defense.

8.3 Department of Defense (DoD) Directive 5000.1 and Instruction 5000.2 (1991). Washington, DC, February 23.

8.4 The NASA Mission Design Process (1992). Washington, DC: National Aeronautics and Space Administration, NASA Engineering Management Council.

8.5 Phase C/D Requirements Specification for the Earth Observing System Data and Information System (EOSDIS) (1990). Greenbelt, MD: Goddard Space Flight Center.

8.6 EDOS Contract Data Requirements List and Statement of Work (1992). Green-belt, MD: Goddard Space Flight Center.

8.7 CDOS Requirements Specification, Level 3 (1990). Greenbelt, MD: Goddard Space Flight Center.

8.8 Integrated Computer-Aided Software Engineering (I-CASE) Solicitation (1992). Gunter AFB, AL: Department of the Air Force, Standard Systems Center.

8.9 Mission Oriented Information System Engineering (MOISE) Solicitation, Request for Comment (1992). Washington, DC: U.S. Coast Guard, Department of Transportation.

8.10 Eisner, H. (1988). Computer-Aided Systems Engineering. Englewood Cliffs, NJ: Prentice Hall.

8.11 Requirements Analysis & Design Tool Report (1992). Hill AFB, UT: U.S. Air Force, Software Technology Support Center.

8.12 Davis, A. (1990). Software Requirementsâ€”Analysis and Specification. Englewood Cliffs, NJ: Prentice Hall.