1. Chapter 9: Systems architecting: Principles (pt. 3) ISE 443 / ETM 543 Fall 2013

2. There are a number of considerations when architecting large, complex systems... 2 443/543– 9 The “95% solution” Trade-offs Sensitivity analysis Modeling and simulation

3. The “95% Solution” refers to a formal way of negotiating a relaxation in requirements A way of challenging “extreme requirements” In addition to “Low Cost”, “Baseline”, and “High Effectiveness” option  Meets “most” of the requirements Presented as an additional option that will Lower overall cost Improve overall performance Improve chances of meeting schedule  Considered in the analysis in the same way as other alternatives Make it clear to the customer  the precise requirements that have not been met  the level of performance that is achieved with respect to these requirements 3 443/543– 9

4. When defining system architectures, a number of trade-off decisions will be made From MIL-STD 499B  “Trade-off studies shall be defined, conducted and documented at the various levels of functional or physical detail to support requirements, functional decomposition/allocation, and design alternative decisions or, as specifically designated, to support the decision needs of the systems engineering process.” Used to make decisions in a number of areas (see pg. 288) See section 9.7.2 (starting on pg. 288) for an in-depth example 4 443/543– 9

5. The final architecture selection should always be subjected to a sensitivity analysis The results of the analysis will be sensitive to a. The selection of criteria b. The weighting of these criteria c. The ratings of each system For this reason, we conduct a sensitivity analysis... 1. Identify the range of possible weightings for each criterion (for example, a range from lowest possible to highest possible) 2. Change the weightings of the criteria to reflect the range 3. Rerun the analysis to determine any changes in result Your turn... conduct a sensitivity analysis for your personal computer architecture selection 5 443/543– 9

6. Because systems are complex and there are uncertainties involved, quantitative analyses can be difficult to conduct Modeling and simulation are used at several points in the system architecting process  to estimate the expected performance characteristics for alternative architectures  trade-off analyses  sensitivity analyses Can also be used at a number of different levels  Overall architecture  Subsystem design  Component and material selection The validity of the results will depend on the accuracy and appropriateness of the model(s) 6 443/543– 9