《系统工程第三章》

1、系统工程第三章PPT课件1 Chapter3 Formulation of Issues 2021-4-29系统工程第三章PPT课件2 1 INTRODUCTION It is very important, we believe, that texts on systems engineering and problem solving, in general, pay significant attention to issue formulation, as a step in systems engineering that needs to occur in each of the

2、phases of effort. This is so because, in practice, the results of a poor issue formulation effort may be subject to very detailed analysis, and the results of this are carried over into implementation. As a result, we obtain the wrong system! Needless to say, this usually results in a waste of resou

3、rces and (through engineering) an inferior system, compared to that which might have resulted from a better issue formulation. Issue formulation is critical across the definition, development, and deployment phases of a systems engineering life cycle. This is not a step implemented only as part of t

4、he systems definition phase, although it is very important in that phase. 2021-4-29系统工程第三章PPT课件3 1 INTRODUCTION A problem, or an issue as a generally synonymous term, can usually be viewed from several perspectives, and the solution that results will often be a strong function of the perspectives fr

5、om which a problem is viewed and formulated. 2021-4-29系统工程第三章PPT课件4 1 INTRODUCTION Issue formulation begins with a definition of the problem or issue to be resolved. This includes an assessment of the situation surrounding the problem. Situation assessment is important in problem solving and issue r

6、esolution. There are many aspects of the environment surrounding an issue that we need to know about in order to be able to generate potentially feasible alternative courses of action that can lead to issue resolution. Many of these factors are dynamic, uncertain, and subject to change with the pass

7、age of time. Situation assessment means that we need to make a careful appraisal of the various factors that influence a particular observed state or condition. Generating good alternatives, ones that truly satisfy the needs of our customers in an effective, efficient, equitable, and explicable mann

8、er, depends on an indepth situation assessment. 2021-4-29系统工程第三章PPT课件5 2 SITUATION ASSESSMENT Complete situation assessment consists of three basic steps that are intended to answer the three questions highlighted in Figure 3.1. 2021-4-29系统工程第三章PPT课件6 2 SITUATION ASSESSMENT nThe first part is the id

9、entification of the (immediate) past in terms of the question, What was? nThe second part of a situation assessment examines the current status or position of things relative to the goal. It is a descriptive component and answers the question, What is? nThe third or normative component of a situatio

10、n assessment answers the question, What ought to be? Understanding of the major, ideally all, factors influencing the past, present, and future is needed for a good situation assessment. There is a horizon component of situation assessment and it answers the question, What factors over time matter a

11、nd when do they matter? 2021-4-29系统工程第三章PPT课件7 2 SITUATION ASSESSMENT We have a complete situation assessment once we know the following: nWhat do we want to accomplish? nWhat is the past and current state of affairs relative to our goal brought about by the changed situation? nWhat are the relevant

12、 factors that influence the situation and their associated time frame. 2021-4-29系统工程第三章PPT课件8 2 SITUATION ASSESSMENT There are a large variety of environments in which various systems must operate. A number of different perspectivessuch as technical, economic, legal, political, cultural, and socialc

13、an be important for understanding a systems environment. When an adequate appreciation of all the important perspectives is achieved, then we say we have preserved the contextual integrity of the issues under consideration. The problem of issue definition, and the resulting identification of worthwh

14、ile alternatives, depends on an accurate and timely situation assessment that preserves this contextual integrity. 2021-4-29系统工程第三章PPT课件9 2 SITUATION ASSESSMENT Accomplishing a high-quality situation assessment depends on several factors. First, the experiential familiarity with the issues or proble

15、m under consideration is very important. For example, it is unlikely that someone with very little background knowledge about nuclear power plants would be able, without considerable study, to develop useful alternatives for ensuring safe operation of such a facility. As we have already noted, knowl

16、edge is information in a relevant context. 2021-4-29系统工程第三章PPT课件10 2 SITUATION ASSESSMENT But you need more than just knowledge about the specific problem or issue at hand. Familiarity with the environment into which the specific issue or problem is embedded is also crucial to an understanding of co

17、ntext. For example, the design of a successful information system for airline reservation agents is made much easier by someone with an indepth knowledge of the various tasks that such agents perform and the environment that agents must cope with as they perform these tasks. You could learn a lot ab

18、out designing such a system from someone who is an expert at developing human- computer interfaces. But you can also appreciate how helpful it would be to interview some experienced ticket agents and to find out about the difficulties they experience when talking to customers and booking their fligh

19、ts. It is the job of systems engineers to make sure that the relevant knowledge of experienced people is brought into a project and used in issue formulation. Capturing this knowledge often requires the systems engineer to skillfully conduct both individual interviews and group meetings. 2021-4-29系统

20、工程第三章PPT课件11 2 SITUATION ASSESSMENT A normative scenario describes how the stakeholders want the system to be in the future. This is not as easy to accomplish as it might appear to be. nWe will often need to distinguish between realistic needs and frivolous wants. nOften also, important stakeholders

21、 have conflicting opinions on what the future should be, or on b. nSome have unrealistic expectations of what technology can deliver in the time frame（期限） under consideration. nOthers are reluctant to see any changes because they think their job or relationship to a system may be put in jeopardy（危险）

22、. A skilled systems engineer must broker these various interests to create enthusiasm and support for a technically feasible, trustworthy project. One way of gaining support for an improvement to an existing system or for a completely new system is to involve stakeholders in the process. Helping peo

23、ple visualize the future in meaningful ways will go a long way toward creating a useful normative scenario. 2021-4-29系统工程第三章PPT课件12 2 SITUATION ASSESSMENT But how can you see into the future? Besides talking to key people, another way of accomplishing a situation assessment is to observe the current

24、 system, if one exists. An objective appraisal of the problems with the current system can be very helpful. A simple listing of these observations in a log book by date and time is often worthwhile. Be sure to note the main ideas of people managing and working with the system. Often, problems will n

25、ot be evident on the first visit. Subsequent visits will reveal more. People also are more open with you after they get to know you and feel comfortable with you. Information gained by observing the current system and talking to people involved with it is most valuable for writing a descriptive scen

26、ario. A descriptive scenario tells why the current system came into being, how it works, and what problems are associated with it. You should include the main actors or stakeholders involved with the current system in your descriptive scenario. These stakeholders will usually be owners, users, custo

27、mers, clients, managers, maintainers, administrators, and regulators of the current system. But, for a complete situation assessment you will also need a normative scenario. 2021-4-29系统工程第三章PPT课件13 2 SITUATION ASSESSMENT If there is not a current system to observe, then you need to create a way of s

28、eeing how an entirely new system might work. A number of useful ways exist for this. A group of people with relevant knowledge can meet and talk through how a new system might work. 2021-4-29系统工程第三章PPT课件14 2 SITUATION ASSESSMENT Many other ways exist for examining possibilities for new systems. Prot

29、otypes 3,4 can be built and potential users can experiment with them through simulation. A prototype is a first-cut approximation of what a new system might be. The purpose of a prototype is to quickly gain information from the user about what seems to work and what is needed. For example, a prototy

30、pe of a new information system might be a set of screens that a user could view and comment as to how useful the screens are in helping provide needed information. 2021-4-29系统工程第三章PPT课件15 2 SITUATION ASSESSMENT A model of the situation, and the resulting simulation of operations using the model, can

31、 emulate the operation of a new system. To build a simulation requires a model or some representation of the new system. The usual purpose of a simulation is to get an idea of how the new system might actually work if it were put into operation. For example, a city wanting to build an airport at a n

32、ew location might like to know if the land available can accommodate the number of planes that they anticipate will be landing and taking-off from their new facility. A simulation of an airport that fits within the citys land constraint can be tested to see if any airport layouts can successfully me

33、et anticipated passenger and freight demands. 2021-4-29系统工程第三章PPT课件16 3 APPROACHES TO SITUATION ASSESSMENT Noble says that situation assessment includes the following: nAn estimate of the purpose of activities in the observed situation nAn understanding of the roles of the participants in these acti

34、vities nInferences about completed or ongoing activities that cannot be directly observed nInferences about future activities 2021-4-29系统工程第三章PPT课件17 3 APPROACHES TO SITUATION ASSESSMENT The notion of a threshold is often very important in situation assessment. We might have a threshold for a situat

35、ion, and observing this threshold might be all that is required. When the situation descriptor values exceed this threshold, we might then decide to assess it in greater detail. nIf it is benign, we may choose to ignore it; n if it is not benign, we may decide to react to it or continue to observe i

36、t. A reasonably good illustration of this is the situation assessment of temperature of the human body. One of the potential difficulties relative to observing a situation is that we wish to be able to interactively and proactively deal with issues and not simply to react to difficulties after they

37、have eventuated. 2021-4-29系统工程第三章PPT课件18 3 APPROACHES TO SITUATION ASSESSMENT The general situation assessment process , illustrated in Figure 3.2, be described by the following eight steps: nWe make general observations of as many pertinent（有关的） aspects of the situation around us as is possible in

38、order to identify or confirm the descriptive scenario or status quo（现 状）. nWe see if this information indicates a change in the current situation. If there is no change, we go back to step 1. If there is a change, we proceed to step 3. nWe identify or formulate a number of alternative hypotheses tha

39、t may describe the new situation, or descriptive scenario. I.We attempt to determine if any more information inputs are required for deciding which alternative hypothesis is the most likely one. 2021-4-29系统工程第三章PPT课件19 3 APPROACHES TO SITUATION ASSESSMENT nWe obtain the required information from suc

40、h input sources as a priori predefined stored information, human observations, human knowledge, or sensor measurements. nWe process this information and knowledge to confirm or disconfirm each of the alternative hypotheses. nWe identify the hypotheses with the highest probability (ies) of being true

41、 and identify the associated situation assessment with some appropriate quantification of our confidence in the assessment. nWe determine if the assessment confidence for describing the situation is sufficiently high. If it is not, we go back to step 3 or 4 and repeat the assessment process until th

42、e confidence threshold is achieved. When it is, we have assessed the situation and we go on with the rest of the problem-solving or issue formulation process. 2021-4-29系统工程第三章PPT课件20 3 APPROACHES TO SITUATION ASSESSMENT 2021-4-29系统工程第三章PPT课件21 3 APPROACHES TO SITUATION ASSESSMENT One of the most dif

43、ficult problems in complex decision situations is gathering the appropriate information and properly assessing the situation. Mason and Mitroff are among the many who have commented on this reality. These authors identify three types of errors that can occur in assessing a situation: nType I errors

44、are errors that result from incorrectly assessing that there is a problem when there is no problem. nType II errors are errors that result from incorrectly assessing that there is no problem when there is a problem. nType III errors are errors that result from correctly assessing that there is a pro

45、blem, but incorrectly identifying the nature of the problem. 2021-4-29系统工程第三章PPT课件22 3 APPROACHES TO SITUATION ASSESSMENT nType I errors are generally called false alarms; nType II errors are called misses or missed problem errors; nType III errors cannot generally be overcome by even the best metho

46、ds of problem solving because one is solving the incorrect problem. Only by some rare fortuitous (幸运)circumstance would one ever end up with an appropriate solution for the real problem at hand after misdiagnosis and implementing a course of action for the wrong problem. A major reason for situation

47、 assessment is to avoid Type III errors. 2021-4-29系统工程第三章PPT课件23 3 APPROACHES TO SITUATION ASSESSMENT Type III errors occur most frequently when problems are ill-structured. In this context, it is likely that the most difficult step in the decision process would be the problem definition or situatio

48、n assessment. Complex problems are those problems that require multidisciplinary perspectives if Type III errors are to be minimized. A problem is ill-structured when one or more of the decision alternatives, decision outcomes, values or weights of importance of the outcomes, or the probabilities of

49、 the various outcomes that result from implementing various alternative courses of action are either unknown, imprecisely known, or uncertain. 2021-4-29系统工程第三章PPT课件24 3 APPROACHES TO SITUATION ASSESSMENT Briefly, an ill-structured problem is one in which it is difficult, if not impossible, to reach

50、a consensus(一致同 意) regarding the basic definition of the problem and its possible solutions. Virtually all real-world problems are ill-structured, and it is these problems for which structured situation assessment aids are most needed. We have outlined some of the considerations that need to be give

51、n to establishing situation assessment aids for these problems. 2021-4-29系统工程第三章PPT课件25 4 PROBLEM OR ISSUE IDENTIFICATION The toughest part of most systems engineering efforts is identifying the problem correctly. Many engineering efforts, although they may represent great feats of engineering skill

52、, fail because they were designed to solve the wrong problem or because the implemented solution created more problems. 2021-4-29系统工程第三章PPT课件26 3 PROBLEM OR ISSUE IDENTIFICATION For example, consider the Aswan Dam in Egypt built in the 1960s. Hundreds of the Soviet engineers set about and successful

53、ly built one of the biggest dams and hydroelectrical facilities in the world. However, as the Egyptians soon found out, the effort was, in many respects, a grand failure because it destroyed much of the precious（宝贵的）（宝贵的）, arable（可耕种的）（可耕种的） land in the Nile River Valley. The Nile Rivers natural flo

54、oding process had continually replenished（）（）the soil downstream and made it possible for many crops to grow in fertile river- bottom land. Once the dam was in place, the natural floods no longer replenished the land and vast amounts of formerly rich agricultural land was lost forever. Egypt, which

55、had been able to feed itself, soon became dependent on food exports. Furthermore, the dam flooded forever many priceless ancient ruins under deep water that were upstream from the massive dam. 2021-4-29系统工程第三章PPT课件27 4 PROBLEM OR ISSUE IDENTIFICATION Why didnt the engineers consider the upstream and

56、 downstream impacts of the project? We can guess that the narrow perspective taken by the engineers led them to conclude that the problem was to block tremendous amounts of water behind a dam for generating electricity and preventing floods. This led to the solution of one problem and the creation o

57、f more significant problems. A broader perspective of the problem would have accounted for the upstream ancient ruins and the downstream arable lands and, potentially, averted this travesty. A systems engineer must always consider the potential new problems or ramifications caused by any proposed so

58、lution to the original problem. 2021-4-29系统工程第三章PPT课件28 4 PROBLEM OR ISSUE IDENTIFICATION As the Aswan Dam case shows, identifying a problem or issue for a large-scale project is not easy because there is not just one simple question to solve or difficulty to resolve. The large-scale projects that s

59、ystems engineers work on require the identification of multiple questions or difficulties that must be answered or resolved. And there is not a single correct answer. Instead, there are usually a number of alternatives that can be devised depending on which difficulties the stakeholders believe to b

60、e most important. 2021-4-29系统工程第三章PPT课件29 4.1 Scoping and Bounding the Problem how can you successfully identify the relevant questions and difficulties in a large-scale project? Properly scoping and bounding a systems engineering effort is the answer. To scope a project means to understand why the