Each model shows a series of cause-and-effect relationships. We encounter such relationships every day. For example, pressing the accelerator causes the car's speed to increase. Pressing the pedal is the 'cause' and the increase in speed is the 'effect.' But the opposite is also true...releasing the accelerator pedal causes the car's speed to decrease. Either way you look at it, the relationship between the accelerator pedal and the car's speed is a direct relationship. Whichever way the 'cause' goes, the 'effect' follows suit!
There are also inverse relationships although they are not as common. But here is a good example. Pressing on the brake pedal causes the car's speed to decrease. And the opposite is also true-- releasing the brake pedal causes the car's speed to increase. Whichever way the brake pedal goes the car's speed does the opposite. This is an inverse relationship.
Each of these situations can be represented symbolically. For example, AP can stand for accelerator pedal and S can stand for the car's speed.
An arrow pointing from the cause (AP) toward the effect (S) could represent
the relationship itself. If we specify that a solid arrow means a direct relationship,
then the symbolism to the left can be interpreted in either of two ways:
In the case of an inverse relationship, such as that
between the brake pedal (BP) and the car's speed (S), the relationship arrow could be
dashed rather than solid (right). This could also be interpreted in either or two ways:
Space is at a premium when crowding many relationships into one model. To save space, share elements when they are common to more than one relationship. For example, the car's speed (S) is a common element in both relationships described above. Therefore, the same "S" symbol can be used in the two cause-and-effect relationships as shown below. Also notice that reading from left to right is not a requirement--the inverse relationship, in this example, is read from right to left.
... click on the "Making Models" link in the HOW TO USE navigation panel before going to any of the topics in the panel at the top of the screen.
Last update:7/21/2005