AGENDA Determining the system classification How much of the system to model What components and events to model What input data to collect What output data to generate with the model SYSTEM CLASSIFICATIONS Discrete versus continuous versus combined… Terminating versus non-terminating … DISCRETE VERSUS CONTINUOUS VERSUS COMBINED Discrete System events occurred according to discrete jumps in the time clock Arrivals, service starts, service ends Continuous The status of components are continuously changing with respect to time Use differential equations to track weights and concentrations Combined Contains both continuous and discrete components Fluids change to discrete units such as cans or boxes TERMINATING VERSUS NON-TERMINATING Terminating systems Have a natural terminating event Not keep entities in the system from one time period to the next Non-terminating systems Have a terminating event, but keep entities in the system between time periods Not have a terminating event and run continuously Statistical analysis approach differs Examples… EXAMPLES OF TERMINATING TYPE SYSTEMS Stores Restaurants Banks Airline Ticket Counters EXAMPLES OF NON-TERMINATING TYPE SYSTEMS Most manufacturing facilities Repair facilities Hospitals HIGH LEVEL FLOW CHARTS Essential tool for defining the system Helps obtain a fundamental understanding of the system logic Graphically depicts how the major components and events interact Based on observations from orientation activities Require a certain level of discipline to create before jumping into programming STANDARD FLOW CHART SYMBOLS Oval Rectangle Tilted parallelogram Diamond OVAL Used to designate both the start and stop processes First and last symbol on the chart Start has only one way out from the bottom or side Stop has only one way in from the top or side RECTANGLE Used to represent general purpose processes Entered from the top or the left side Exited from either the bottom or right side Examples A service time delay TILTED PARALLELOGRAM Used for processes which involve some sort of input or output Entered from the top or the left side Exited from either the bottom or right side Example Creation or arrival of entities into a system DIAMOND Used to represent a decision in the flowchart logic One input connector, Two output connectors Input connector should come into the top vertex Output can leave through either of the side vertices or the bottom vertex Output connectors are labeled as either True or False Yes or No Only one output path may be taken SAMPLE HIGH LEVEL FLOW CHART A single queue, single server system SIMPLE PROCESS SYSTEM COMPONENTS TO MODEL The model must contain enough content to be properly understood A limited amount of time is available for most projects Begin with a coarse model and add refinements later SPECIFIC SYSTEM COMPONENTS Personnel… Machines… Transporters… Conveyors… PERSONNEL Sales clerks Customer service representatives Machine operators Material handlers MACHINES Service systems… Manufacturing systems… MACHINES IN SERVICE SYSTEMS Computer or network systems Automatic teller Ticket machines Scanners X-ray machines MACHINES IN MANUFACTURING SYSTEMS Computer numerically controlled mills Machining centers Lathes Turning centers Robots TRANSPORTERS Service Systems… Manufacturing Systems… TRANSPORTERS IN SERVICE SYSTEMS Airplanes Buses Trains TRANSPORTERS IN MANUFACTURING SYSTEMS Forklifts Hand trucks Dollies Automatically guided vehicles CONVEYORS Service Systems… Manufacturing Systems… CONVEYORS IN SERVICE SYSTEMS Moving sidewalks Escalators Chair lifts CONVEYORS IN MANUFACTURING SYSTEMS Overhead crane systems Fixed production assembly lines PROCESS AND EVENTS TO MODEL Service Manufacturing PROCESSES AND EVENTS IN SERVICE SYSTEMS Arrival of customers at a processing area… Customer queue behavior… Service processing … Payment for the goods… ARRIVAL OF CUSTOMERS AT A PROCESSING AREA Interarrival times of batch Batch sizes QUEUE BEHAVIOR Types of queues Queue priorities Queue entity behavior TYPES OF QUEUES Parallel queues Single snake queues QUEUE PRIORITIES First-in-first-out (FIFO) Last-in-first-out (LIFO) Shortest processing time (SPT) Longest processing time (LPT) Lowest value first (LVF) Highest value first (HVF) User defined rules QUEUE ENTITY BEHAVIORS Balking Reneging Jockeying SERVICE PROCESSES Retail Service Checkout Processes… Banking Service Processes Restaurant Service Processes Airline Ticket Counters Service Processes RETAIL SERVICE CHECKOUT PROCESSES Calculating the cost of goods Payment CALCULATING THE COST OF GOODS Number of goods being purchased Type of goods being purchased PAYMENT PROCESS Cash Check Credit Debit Account MANUFACTURING SYSTEM PROCESSES AND EVENTS Types of work Orders Machine Queue Behavior Machine Processing Machine Buffers Material Transportation Machine Failures Preventive Maintenance Product Inspection Failures EVENTS NOT TO MODEL Events with very limited impact on the system outputs As a result of the small importance or infrequent occurrence of the event Examples Discovery of an explosive device in a security checkpoint system Power outage in a manufacturing facility Shuttle bus being involved in an accident Workers going on strike TYPES OF INPUT DATA TO COLLECT Entity related Resource related ENTITY RELATED INPUT DATA Interarrival times Batch sizes Classifications Balking, reneging, and jockeying Movement times RESOURCE RELATED INPUT DATA Service times Break times Failure rates Scheduled maintenance Movement times OUTPUT DATA Measures of performance Average time in the system Average time in a queue Time average number in queue Average utilization rates Counters