【正文】 Instead, there are usually a number of alternatives that can be devised depending on which difficulties the stakeholders believe to be most important. 上午 4時 12分 2022 SYSTEMS ENGINEERING 29 Scoping and Bounding the Problem how can you successfully identify the relevant questions and difficulties in a largescale project? Properly scoping and bounding a systems engineering effort is the answer. To scope a project means to understand why the project is necessary, what the stakeholders intend to acplish with the project, and how to measure project success. In systems terms, this means identifying the needs, objectives, and criteria for the project. The needs tell why the project is necessary. Related to the needs, the objectives describe in detail everything that the project is intended to acplish. Criteria measure success in achieving the objectives. 上午 4時 12分 2022 SYSTEMS ENGINEERING 30 Scoping and Bounding the Problem To bound a project means to understand the limitations associated with the project, the changes that can be made to achieve desired objectives, and the important quantities that are likely to change as a result of the project. In systems terms, this means identifying the constraints, parameters, and variables for the project. Constraints are the limits that must be observed for the project. Constraints include realistic considerations related to things such as money, time, people, anizations, and society. For example, most projects have budget, time deadlines, and environmental impact constraints. 上午 4時 12分 2022 SYSTEMS ENGINEERING 31 Scoping and Bounding the Problem Parameters are factors that define an alternative and determine its behavior. The value to which parameters are set restrict what results are possible to achieve with an alternative. For example, in the design of a mass transit system for a city, some parameters might be the number of buses and trains. How many people can be moved by any specific mass transit alternative depends on the value to which these parameters are set—how many buses and trains there are for an alternative. Once a system is in operation, parameters do not change much. Every day that the city operates the mass transit system, the same number of buses and trains are part of the system. Parameters are factors that the systems engineer manipulates to create alternatives and alter their performance. To distinguish parameters from the quantities associated with mathematical models, you can refer to them as alterables. 上午 4時 12分 2022 SYSTEMS ENGINEERING 32 Scoping and Bounding the Problem In contrast to parameters, response variables are likely to change once the system is in operation. Variables are measurable quantities that you want to monitor as the system operates. For example, the number of passengers that use the buses or trains each day is a response variable that changes as the system operates. For largescale systems the number of such variables can be overwhelming. That is why we use the concept of state variables. 上午 4時 12分 2022 SYSTEMS ENGINEERING 33 Systems Definition Matrix State variables are a collection of response variables that we choose to monitor to inform us about the status of a system. The specific variables chosen depend on why we want the information. If we are system engineers investigating the adequacy of a currently existing mass transit system, then we probably want to know a number of variables at different times of the day and week. For example, two state variables might be the number of passengers per route and the number of operational buses and trains. 上午 4時 12分 2022 SYSTEMS ENGINEERING 34 Systems Definition Matrix A convenient way for the systems engineer to document the scoping and bounding of a problem is to use a systems definition matrix like the one shown in Figure . The matrix has two main sections. One section defines the scope of the project by listing the needs, objectives, and criteria. The other section lists the parameters, variables, and constraints and defines the bounds of the project. The simple framework of the systems definition matrix is useful as a checklist for information gathering, documentation, and munication. 上午 4時 12分 2022 SYSTEMS ENGINEERING 35 Systems Definition Matrix The simple matrix suggested here can be expanded to include more features and elements of a proposed system or project. For example, the purposes and basic functions of a system, its inputs, outputs, major ponents, human agents, environment, super and lateral systems, and interfaces and controls could all be dimensions of the system that are described in the matrix. 上午 4時 12分 2022 SYSTEMS ENGINEERING 36 Systems Definition Matrix If you want to put more details in the matrix, you can create a systems definition matrix for each subsystem of the larger system. For a multiproject program, you might want to plete a system definition matrix for each major project in the program. For a multistage project, you may want to plete a matrix for each phase of the project. Additionally, you can use these matrices to help you identify and specify the interactions among the various ponents. 上午 4時 12分 2022 SYSTEMS ENGINEERING 37 Systems Definition Matrix The system definition matrix, when plete, should give you and those that you need to municate with a thorough picture of the basic ingredients of an existing or proposed system. It can help you to discover insights into the feasibility and internal consistency of a proposed d