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principles:model_principle [2018-12-08 11:54]
christian example 5
principles:model_principle [2019-12-31 20:31] (current)
68.72.140.10 [Description]
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 ===== Description ===== ===== Description =====
  
-The software should model and mirror the "real world"​. This first of all means, that the structure of the software---to some extend---models the structure of the problem. When the "real world action"​ that the software should support comprises certain entities like e.g. customers, products, and orders, then there should be one object for each customer, product and order. Furthermore there should be one class for each concept. And if there is a certain relationship between customers, orders, and products, there should also be an association between the corresponding classes and references between the objects. So the object structure models the structure of the real world concepts.+The software should model and mirror the "real world"​. This first of all means, that the structure of the software---to some extent---models the structure of the problem. When the "real world action"​ that the software should support comprises certain entities like e.g. customers, products, and orders, then there should be one object for each customer, product and order. Furthermore there should be one class for each concept. And if there is a certain relationship between customers, orders, and products, there should also be an association between the corresponding classes and references between the objects. So the object structure models the structure of the real world concepts.
  
 Real world actions are then //​mirrored//​ in the software system. This means that each action in the real world triggers a corresponding action in the model world which ensures that the model stays consistent with the real world. So the software is a kind of a simulation of what actually happens. If customer orders some product, the software reacts by creating an order object, which is connected to the customer and the product objects corresponding to the customer and the product involved in the real world action. Real world actions are then //​mirrored//​ in the software system. This means that each action in the real world triggers a corresponding action in the model world which ensures that the model stays consistent with the real world. So the software is a kind of a simulation of what actually happens. If customer orders some product, the software reacts by creating an order object, which is connected to the customer and the product objects corresponding to the customer and the product involved in the real world action.
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-==== Example 4: Break and Air Conditioning ====+==== Example 4: Brake and Air Conditioning ====
  
-Suppose a car has an air conditioning and a hill start assistant. The air conditioning needs to make sure that the engine provides enough power on sunny days. So it measures its power-consumption and pushes down the gas pedal just enough to the engine isn't stalled. The hill start assistant automatically releases the hand break if you start driving. Now the following situation can happen: A car waits in front of a boom barrier of an underground garage. It's a hot day and the driver opens the window to get the ticket. hot air flows into the car and the A/C powers up. The revolution speed is low because the car stands still so the A/C hits the gas pedal in order not to stall the engine. Now the hill start assistant realizes that the gas pedal was pressed and releases the hand break because pressing the gas pedal is the trigger that the diver want to drive away. As a result the car crashes into the boom barrier.+Suppose a car has an air conditioning and a hill start assistant. The air conditioning needs to make sure that the engine provides enough power on sunny days. So it measures its power-consumption and pushes down the gas pedal just enough to the engine isn't stalled. The hill start assistant automatically releases the hand brake if you start driving. Now the following situation can happen: A car waits in front of a boom barrier of an underground garage. It's a hot day and the driver opens the window to get the ticket. hot air flows into the car and the A/C powers up. The revolution speed is low because the car stands still so the A/C hits the gas pedal in order not to stall the engine. Now the hill start assistant realizes that the gas pedal was pressed and releases the hand brake because pressing the gas pedal is the trigger that the diver want to drive away. As a result the car crashes into the boom barrier.
  
 The problem here is with the A/C. Semantically it wanted to increase the motor power but actually it called an operation that hit the gas pedal. This is almost the same but not exactly the same. It's an operation on the wrong level of abstraction. If the A/C had called an operation ''​increaseMotorPower''​ instead of an operation ''​hitGasPedal''​ the problem would have been prevented. ​ The problem here is with the A/C. Semantically it wanted to increase the motor power but actually it called an operation that hit the gas pedal. This is almost the same but not exactly the same. It's an operation on the wrong level of abstraction. If the A/C had called an operation ''​increaseMotorPower''​ instead of an operation ''​hitGasPedal''​ the problem would have been prevented. ​
principles/model_principle.1544266450.txt.gz · Last modified: 2018-12-08 11:54 by christian