1. The SIMILAR Process A. Terry Bahill Emeritus Professor of
11/9/2018
The SIMILAR Process
A. Terry Bahill
Emeritus Professor of
Systems Engineering
University of Arizona
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2. Reference
Bahill, A.T. and Gissing, B. "Re-evaluating systems engineering concepts using systems thinking," IEEE Transactions on Systems, Man, and Cybernetics, Part C Applications and Reviews, 28(4), ,
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4. My way for doing everything
The SIMILAR process is a life-cycle model. But, it is not a serial process. It is parallel and highly iterative.
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5. The SIMILAR Process
State the problem Investigate alternatives Model the system Integrate Launch the system Assess performance Re-evaluate
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6. Customer needs and expectations
The customer is more concerned with the product’s capabilities than with detailed product requirements & specifications
What the product will do; how it fills a need
Requirements stated in a Request for Proposal (RFP) are often vague and incomplete; sometimes even contradictory
The engineers’ challenges:
Understanding what the customer really needs
Understanding which requirements are firm and which are negotiable areas for tradeoffs
Who is the customer?
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8. Stakeholder needs and expectations can change over time due to:
Cost / benefit tradeoffs
Technological advances or limitations
A better understanding of the feasibility and consequences of original requested capabilities
Information uncovered during the design process
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9. The problem statement Specifies the system’s mission
Explains the customers’ needs and expectations
States the goals of the project
Defines the business needs
Prescribes the system’s capabilities
Delineates the scope of the system
Expresses the concept of operations
Describes the stakeholders
Presents the key decisions that must be made
Shows the suggested architecture
Highlights the preferred alternatives
Should be in terms of what must be done, not how to do it
Summarizes the four most important program metrics: performance, cost, schedule and risk
Lists the deliverables: what will be delivered to whom and when
Is written in plain language and is intended for management and the public.
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10. The beginning
“The beginning is the most important part of the work,” Plato, The Republic, 4th century B. C.
“All the really important mistakes are made the first day,” Eb Rechtin, The Art of System Architecting, 2000.
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11. Investigate alternatives
Investigating alternatives is more than making a list.
Alternative designs are evaluated for performance, cost, schedule and risk (and even customer acceptance).
Evaluations are based on analyses, simulations, prototype testing, etc. and are updated as new information becomes available
Alternatives may be evaluated in parallel or in series.
Consideration of alternatives clarifies the requirements and reduces risk.
Remember to include the do nothing alternative!
But – if the do nothing alternative wins, perhaps you did not assign sufficient weight to performance.
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12. Model the system
Models should be developed for most alternative designs.
There are many types of models, for example physical analogs, analytic equations, state machines, functional flow block diagrams, block diagrams of linear systems theory, transfer functions, state space models, differential or difference equations, object-oriented models, UML diagrams, Monte Carlo…
Models for the preferred design will be expanded, refined & validated throughout the product life cycle.
Running models clarifies requirements, reveals bottlenecks and fragmented activities, reduces cost and exposes duplication of efforts.
Models also support risk and reliability analysis.
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13. Integrate
Systems, businesses and people must be integrated so that they interact with one another. Integration means bringing things together so they work as a whole.
Subsystems and interfaces between subsystems must be designed to work properly as an integrated system.
A key systems engineering role is the design and management of system interfaces.
Both internal interfaces within the system and external interfaces to the outside.
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14. Launch the system
System launch means running the system in its operational environment, or exercising the model in a simulated environment to produce outputs necessary for evaluation.
In a manufacturing environment, this means modifying and using commercial-off-the-shelf hardware and software, writing prototype code, and/or bending metal.
In the business environment, this means is decomposing the business plan into tasks and actions.
The purpose of system launch is to provide an environment that allows the system or its model to do what it is being designed to do.
launching includes delivery, installation, acceptance testing, training, and support
product and process
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15. Assess performance
Evaluation criteria (often called figures of merit or measures of effectiveness) are used to quantify requirements and in tradeoff studies.
Technical performance measures are used to mitigate risk during design and manufacturing.
Metrics are used to help manage a company's processes.
Measurement is the key. If you cannot measure it, you cannot control it. If you cannot control it, you cannot improve it.
Testing and conducting design reviews contribute to performance assessment
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16. Re-evaluate
Re-evaluate means observing outputs and using this information to modify the system inputs, the product or the process.
Re-evaluation is the most important of these functions.
Re-evaluation should be a continual process with many parallel loops.
Re-evaluate both the work products and the process itself.
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17. State the problem
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18. Investigate alternatives
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19. Model the system
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20. Assess performance
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21. Re-evaluate
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22. Product and process
The first step in describing a process should be describing the product of that process. However …
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23. Processes Product quality is a direct result of good processes.
Only stable processes can be improved.
Define how much process variability is acceptable.
Reduce process variability.
To know if you have improved quality, everyone must be using the process the same way, using the same metrics.
Processes must have a built-in process to improve the process.
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24. Processes should be Documented Measurable Stable Of low variability
Used the same way by all
Adaptive
Tailorable!
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25. Each process must be tailored1
A standard process is illusory in some cases. For tried and true activities where the goal is similar to previous goals, and the resources and circumstances are the same, then a standard process works great.
Try to bake a cake without a standard process and see what you get. But realize that under high altitude or low humidity conditions, you must adjust the process and perhaps the ingredients to have a successful cake.
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26. Each process must be tailored2
There is a key difference between a mere cook and a true chef. The cook can only blindly follow the process. A chef can tailor the recipe to fit the situation and the chef is aware of the big picture in terms of the entire meal, the entire experience. A good chef will know what types of cakes go well with what types of entrees, and how they contribute to the whole purpose of the dining event.
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27. Each process must be tailored3
So, a process is neither necessary nor sufficient for successful development. However, it does contribute to more effective use of limited resources (cost, schedule, people) if used wisely and judiciously. There is a difference between knowledge and wisdom. Knowledge of process is not enough.
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28. Processes must be managed
Each process must be managed with adaptive, learning, feedback control loops.
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29. What is not a part of SIMILAR?
Inspections of final products
Inspections are old fashioned
You cannot inspect in quality
To improve quality you must change processes or behavior.
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30. Conclusions
Many authors have shown processes with fundamental similarities. These similarities were encapsulated with the SIMILAR Process.
Using the SIMILAR Process can help eliminate redundant or extraneous functions, and can help ensure inclusion of necessary functions.
There is a process for doing systems engineering.
When you are asked to describe a process, make your description look like the SIMILAR Process.
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31. The SIMILAR process
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