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CHAPTER ELEVEN Dr. Rami Gharaibeh BUSINESS SIMULATION.

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Presentation on theme: "CHAPTER ELEVEN Dr. Rami Gharaibeh BUSINESS SIMULATION."— Presentation transcript:

1 CHAPTER ELEVEN Dr. Rami Gharaibeh BUSINESS SIMULATION

2 Dr. Rami Gharaibeh simulation is useful for training, persuasion, and analysis. Simulation is also useful for model validation—for finding and fixing errors in a model. CHAPTER ELEVEN benefits

3 Dr. Rami Gharaibeh Example you seek to enhance customer satisfaction CHAPTER ELEVEN simulating a business process model

4 Dr. Rami Gharaibeh Traditionally Mykonos management has thought about customer satisfaction in terms of the quality of the dishes prepared You intend to use your new responsibility to consider customer satisfaction more broadly. want to look at customer wait times and the impact of waits on satisfaction. CHAPTER ELEVEN simulating a business process model

5 Dr. Rami Gharaibeh Customers have many waitings They wait for a table to be available. They wait for water, and bread. They wait for the staff to take their orders. They wait for their food, and they wait for their bills. You are concerned that all this waiting makes customers dissatisfied CHAPTER ELEVEN simulating a business process model

6 Dr. Rami Gharaibeh You will create two models the customer dining process. how customers arrive, are seated, have their orders taken, and so on customer satisfaction. how food quality, wait times, and other factors contribute to customer satisfaction and how word of mouth and restaurant reviews affect the view of potential customers and, ultimately, a restaurant’s success. CHAPTER ELEVEN simulating a business process model

7 Dr. Rami Gharaibeh Working with the models, you could examine the effect of different policies on wait times. And the two models could help communicate the results to the restaurant general manager, ultimately persuading him to change his policies and reduce the wait times. CHAPTER ELEVEN simulating a business process model

8 Dr. Rami Gharaibeh Working with the models, you could examine the effect of different policies on wait times. And the two models could help communicate the results to the restaurant general manager, ultimately persuading him to change his policies and reduce the wait times. CHAPTER ELEVEN simulating a business process model

9 Dr. Rami Gharaibeh After several sessions with the SME the models were developed The simulation shows that each customer party waits 46 minutes on average. This 46 minutes includes all the waits CHAPTER ELEVEN simulating a business process model

10 Dr. Rami Gharaibeh The following figure shows an initial simulation result, a breakdown of the average times spent by customers, organized by activity CHAPTER ELEVEN simulating a business process model

11 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

12 Dr. Rami Gharaibeh Wait times vary over the course of the week. Mondays and Tuesdays see far fewer customers than Fridays and Saturdays, and far shorter waits. CHAPTER ELEVEN simulating a business process model

13 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

14 Dr. Rami Gharaibeh Wait times also vary over the course of a single evening. The wait times are shortest both early and late in the evening and longest in the middle of the evening, when the restaurant is busiest. CHAPTER ELEVEN simulating a business process model

15 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

16 Dr. Rami Gharaibeh after validating the model, we will start the analysis What happens if the staffing is doubled? What happens on Friday nights if there are two hosts available to greet and seat customers instead of one, twice as many servers waiting tables, twice as many chefs cooking meals, and twice as many bartenders mixing drinks? CHAPTER ELEVEN simulating a business process model

17 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

18 Why is the reduction in wait times so modest even when the staff is doubled? Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

19 The law of diminishing returns If we are constrained in one resource, the increase in another resource will bring diminishing returns Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

20 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

21 What happens if the staffing is doubled, and the number of tables is doubled and the kitchen capacity is doubled? Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

22 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

23 Most of the waits have disappeared. the obvious conclusion from this experiment: The restaurant is just not big enough for the demand on busy nights. But, doubling the capacity is not realistic !!! Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

24 a more realistic alternative is to change our policy What if we ask customers to make reservations on busy nights? Here are the results Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

25 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

26 People are in fact waiting less. But that reduced wait comes at a cost: the restaurant is serving fewer people and the bar is serving far fewer drinks to people who are waiting. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

27 Many other experiments are possible. What if the size of the waiting list is no more than three parties at a time? What if we staff a single additional server on Fridays and Saturdays? What if we cross-train the servers, so they could perform as hosts if the host was busy seating people? What if we only seated smaller parties—those of six people or fewer? Dr. Rami Gharaibeh CHAPTER ELEVEN simulating a business process model

28 Preparing a model for simulation requires some additional work beyond what is required to create a static, non-simulated model. But more significantly than the extra work, preparing a process model to be simulated requires additional knowledge. Dr. Rami Gharaibeh CHAPTER ELEVEN activities, resources, and jobs

29 To create a business process simulation you must understand activities, resources, and jobs and the way these three interact with each other. Dr. Rami Gharaibeh CHAPTER ELEVEN activities, resources, and jobs

30 Dr. Rami Gharaibeh CHAPTER ELEVEN activities, resources, and jobs

31 activity is a single step in a larger business process. A resource is a person who performs the activity Server is a role the person plays. A job is something that flows through the process, being worked on by resources and flowing from activity to activity Dr. Rami Gharaibeh CHAPTER ELEVEN activities, resources, and jobs

32 A job is created at a start event and flows over sequence flows and message flows from activity to activity until an end event is reached. When a job reaches an activity, one of two things can happen. Either a resource is available to work the job or no resource is available and the job must wait until a resource is available Dr. Rami Gharaibeh CHAPTER ELEVEN Job cycle

33 While the resource is performing an activity he is not available to do anything else. When the resource is finished the activity, the job and the resource separate. Dr. Rami Gharaibeh CHAPTER ELEVEN Job cycle

34 The resource is available to do something else: the same activity for another job, another activity for the same job, or another activity in another process. Dr. Rami Gharaibeh CHAPTER ELEVEN Job cycle

35 Dr. Rami Gharaibeh CHAPTER ELEVEN Job cycle

36 The simulation engine collects individual statistics as the simulation progresses—statistics about activities, resources, and jobs. These statistics are aggregated into the simulation results Dr. Rami Gharaibeh CHAPTER ELEVEN Collecting statistics

37 The engine collects statistics on each activity, each resource, and each job. Activity statistics include how many times each activity was performed, the average duration of each activity, the total cost of each activity. Dr. Rami Gharaibeh CHAPTER ELEVEN Collecting statistics

38 Activity statistics include how many times each activity was performed, the average duration of each activity, the total cost of each activity. Dr. Rami Gharaibeh CHAPTER ELEVEN Activity statistics

39 Resource statistics include the utilization of each resource, the total amount of work performed by each resource, Dr. Rami Gharaibeh CHAPTER ELEVEN Resource statistics

40 Job statistics include the total cycle time of each job, the total touch time of each job, Dr. Rami Gharaibeh CHAPTER ELEVEN Job statistics

41 Dr. Rami Gharaibeh CHAPTER ELEVEN Collecting statistics

42 Dr. Rami Gharaibeh CHAPTER ELEVEN Collecting statistics

43 To be simulated, activities need additional attributes. Duration is one such attribute. When a job arrives at an activity, how long does the resource work on it? Each activity has a duration attribute that indicates how long jobs need to be worked. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

44 Activity duration can vary in three different ways. duration can vary depending on the details of the job Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

45 The job that models the party of eight needs to be different from the job that models a party of two. For this simulation, jobs need their own model-custom attribute, party Size. A job representing a party of eight will have a party size value of 8, and a job representing a party of two will have a value of 2. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

46 Second, the duration of the activity can vary depending on the details of the resource. A skilled server will serve drinks quicker than a novice because she remembers who ordered which drink. The simulation needs to know that this server is quick, that one is average, and this other one is slow. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

47 For this model, resources need a model-custom attribute, skill Level, to keep track of skill. Values of skill level can then be 1 for an average skill, 0.8 for a quick server, and 1.2 for a slow one. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

48 Suppose we want the duration of Take Dinner Order to consider both the skill of the server and the size of the party. How do we combine those elements? We need to encode the duration as a formula, perhaps like the duration in the following slide Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

49 Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

50 Third, the duration of the activity can vary randomly. Consider the activity Cook Dinner. The duration of Cook Dinner might vary from 20 minutes to 45 minutes, depending on what is ordered. When durations vary randomly, modelers often employ a uniform distribution. Each duration in a uniform distribution within the range is equally likely; 20 minutes is just as likely as 33 minutes and just as likely as 40 or 45. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

51 When durations vary randomly, modelers often employ a uniform distribution. Each duration in a uniform distribution within the range is equally likely; 20 minutes is just as likely as 33 minutes and just as likely as 40 or 45. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

52 It is also possible to use other distributions: a triangular distribution that peaks somewhere in the middle,. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

53 a standard (bell curve) distribution Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

54 or something more sophisticated. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

55 The statistical distributions (e.g., normal, log-normal, exponential, etc.) often lead to higher model fidelity, but they are usually difficult for SMEs to understand. Dr. Rami Gharaibeh CHAPTER ELEVEN activity durations

56 The duration of an activity specifies the work time—the time a person is actually working on a job. But a job can also experience a delay while it is at an activity, time when no one is actually working on the job. A resource delay occurs when there is no resource available to work a job. Dr. Rami Gharaibeh CHAPTER ELEVEN work time and delay time

57 What happens if the resource starts working on the job then the resource becomes unavailable? We use the resourceShift attribute resource- Shift indicates that the job should be given to another resource if the original one becomes unavailable. Dr. Rami Gharaibeh CHAPTER ELEVEN work time and delay time

58 In some situations, the resource should be the same as the one used at the prior activity. The job waits until that particular resource is available. The activity attribute consistentResource is used to indicate this situation Dr. Rami Gharaibeh CHAPTER ELEVEN work time and delay time

59 In addition to resource delays, a job can experience an intrinsic delay. An intrinsic delay is a delay that occurs as part of the normal work of the job. It might take 40 minutes to prepare the dinner: 25 minutes of work and 15 minutes of intrinsic delay. Dr. Rami Gharaibeh CHAPTER ELEVEN work time and delay time

60 When working a single activity, a job can experience both a resource delay and an intrinsic delay. Cook Dinner includes an intrinsic delay as part of the nature of preparing food. If many dinner orders arrive at once, the chef might have more work than he can do, and some of the dinners suffer delays—resource delays—until the others are finished. (Or the chef could be limited by the physical resources of the kitchen) Dr. Rami Gharaibeh CHAPTER ELEVEN work time and delay time

61 Intrinsic delays and resource delays are both delays. In both situations, the job is waiting and no work is being performed. But they are modeled differently. If an activity has an intrinsic delay, its intrinsicDelay attribute will indicate the amount of time that the job is delayed. Resource delay is not specified in an activity attribute. Instead it is a job waiting for a resource to work it. Dr. Rami Gharaibeh CHAPTER ELEVEN work time and delay time

62 A delay can also occur in a flow, either in a sequence flow between activities in the same pool or in a message flow between pools. Dr. Rami Gharaibeh CHAPTER ELEVEN work time and delay time

63 Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

64 In the midst of a simulation, when a job arrives at an exclusive gateway, how does the simulation engine decide which way to send the job? Does this job represent a party that is ordering drinks or one that will move straight to ordering dinner There are three alternative modeling approaches to this question. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

65 The simplest approach is for each of the outgoing sequence flows from the gateway to indicate a percentage of jobs. Each sequence flow has a conditionExpression attribute indicating whether the sequence flow will be taken. One of the sequence flows is a default; it is the flow taken if none of the others is chosen. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

66 For example, suppose 60 percent of the parties order drinks before dinner and 40 percent do not. A job that arrives at the gateway will have a 60 percent chance of taking the lower path and a 40 percent chance of taking the upper path. Each job is evaluated differently, so in the midst of a simulation run, it is possible for four jobs in succession to beat the odds and all take the upper path. But over the course of hundreds of jobs, the actual results will be close to 60/40. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

67 A second way of modeling how an exclusive gateway determines the outgoing path is to examine an attribute of the job. Suppose that each job in this model had a beforeDinnerDrink attribute, indicating whether the party will order drinks before dinner. For some of the jobs this attribute is true and for others it is false. Then for each job, the outgoing sequence flows from Order Drinks? will examine the value of this attribute. Those with a value of false will be sent along the upper path, and those with a value of true will be sent on the lower path. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

68 There are two advantages of driving a gateway using a job attribute instead of probabilities evaluated on the sequence flow. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

69 1 Job statistics can be analyzed and sorted by the job attribute. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

70 2 Attribute-based scenarios can be created. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

71 There is also a third way to model an exclusive gateway: combining the two approaches and making the gateway split depend on both an attribute of the job and on a random percentage. Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways

72 the conditionExpression attribute of the lower outgoing sequence flow from the Order Drinks? Dr. Rami Gharaibeh CHAPTER ELEVEN simulating exclusive gateways


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