44221: Information Systems Lecture 3 (Week 4) Systems Control Concepts By Ian Perry

Ian PerrySlide : Information Systems: Systems Control Concepts Remember This? How can a systems approach help us apply IT in order to control the above process? Money DisappearsCosts Rise Goods are Damaged Budgeting Unspent (unallocated) funds Spent (allocated) funds Funds Remaining?

Ian PerrySlide : Information Systems: Systems Control Concepts The ‘Feed-back Control Loop’ The basic unit of Control for all Processes. Environmental Disturbances Input(s) ActuatorSensor Goal Output(s) Comparator Feed-back Process

Ian PerrySlide : Information Systems: Systems Control Concepts Elements of Control Sensor Monitor/Measure the Output(s) of the Process. Feed-back Communicate the Sensor Measurement to someone/something. Comparator Compare the Sensor Measurement to the Goal (i.e. the desired state of this Process). Actuator Some means of ‘doing something’ in order to effect a change in the inputs to the Process.

Ian PerrySlide : Information Systems: Systems Control Concepts Negative Feed-back is best! Positive feed-back leads to instability. E.g. Cold War US built/deployed nuclear missiles. USSR built/deployed more nuclear missiles. US built/deployed more nuclear missiles. Etc. Negative feed-back leads to stability. E.g. Heating System Temperature rises above thermostat setting. Heating System shuts down. Temperature falls below thermostat setting. Heating Systems fires up again.

Ian PerrySlide : Information Systems: Systems Control Concepts E.g. Stock Control The Goal of the Stockholding Process is to keep the 'correct' amount of any item in stock. enough to satisfy any customer demand. not so many that we might be left holding stock, which: costs us money. we might not be able to sell if customer demand changes. we might end up throwing away if it ‘spoils’.

Ian PerrySlide : Information Systems: Systems Control Concepts The Stockholding Process Do Something? Compare with Goal? Communicate Stock Level Customer Demand INPUT(s)OUTPUT(s) Theft Stockholding Process New StockStock Level Measure Stock Level Goal = 20

Ian PerrySlide : Information Systems: Systems Control Concepts MUST Make a Distinction Between: Measurement extracting data that represents what has happened. Comparison comparing the new measurement to our desired goal(s). Decision Making deciding what to do about it.

Ian PerrySlide : Information Systems: Systems Control Concepts Measurement Count the stock to determine the current Stock Level. Very easy to support with IT. Customer Demand Theft Stockholding Process New StockStock Level Measure Stock Level

Ian PerrySlide : Information Systems: Systems Control Concepts Comparison Check to see how well the process is going. Relatively easy to support with IT. Communicate Stock Level Stockholding Process Compare with Goal? Goal = 20

Ian PerrySlide : Information Systems: Systems Control Concepts Decision Making Make the necessary adjustments. Harder to support with IT. Do Something? Stockholding Process

Ian PerrySlide : Information Systems: Systems Control Concepts All Control Systems suffer from Lag It takes time to ‘notice’ a change in the real world, ‘extract’ the data that represents this change, and ‘process’ this data in order to update our model. Entity Modified Entity Event real world Modified Model Entity of Processing System model our Data Extracted (Transaction)

Ian PerrySlide : Information Systems: Systems Control Concepts Lags in the Feed-back Loop It takes time: for the ‘Process’ to transform ‘Inputs’ into ‘Outputs’. for the ‘Sensor’, ‘Comparator’ and ‘Actuator’ to notice any variation from the ‘Goal’ and effect a change. Environmental Disturbances Input(s) ActuatorSensor Goal Output(s) Comparator Feed-back Process

Ian PerrySlide : Information Systems: Systems Control Concepts E.g. In a Supermarket It takes time: to accept new deliveries of products. place products onto shelves. modify stock levels when customers buy products. compare the actual level of stock for individual products with the desired level of stock. re-order those products that have fallen below their desired level. then, wait for another delivery!

Ian PerrySlide : Information Systems: Systems Control Concepts ‘Accommodating’ the Environment Systems should be designed to exhibit the ‘optimum’ (i.e. best) response to disturbances from the environment. Two new concepts: Buffers E.g. the amount of Product A we must hold in order that we never run out, given that both supply and demand are outside of our control. Control Frequency E.g. the frequency with which we check the stock level of Product A against our desired stock level.

Ian PerrySlide : Information Systems: Systems Control Concepts The ‘optimum’ Stock Level? Holding stock is not automatically undesirable: but, what we don’t want is ‘too much’ or ‘too little’. Cost of Stock-outs Cost of Holding Stock Total Cost Optimum Range Stock Level Lots!0 Cost Lots! 0

Ian PerrySlide : Information Systems: Systems Control Concepts The ‘optimum’ Control Frequency? How often should we check on a process? i.e. measure/compare/decide. Cost of Not Checking Cost of Checking Total Cost Optimum Range Control Frequency ContinuousNever Cost Lots! 0

Ian PerrySlide : Information Systems: Systems Control Concepts Summary Basic unit of control for all processes: the Feed-back Control Loop. Negative Feed-back is best: leads towards stability. Information Technology might help: by speeding-up/automating the measure/compare/decide part of the feed-back loop. Can’t control the Environment: need to ‘accommodate’ disturbances. New concepts: Buffers. Control Frequency. MUST ‘optimise’ both: in order to ‘accommodate’ environmental disturbances. Environmental Disturbances Input(s) ActuatorSensor Goal Output(s) Comparator Feed-back Process Cost B Cost A Total Cost Optimum Controllable Variable Cost