Number of States
Impossible States
Equivalent State
Number of States:
In a state graph, the number of states that is chosen to model is the number of states
The state can be directly or indirectly recorded by combining the values of variables that apperar in the database
The number of states is the product of the number of allowable values of all the factors
Find the number of states as follows:
Identify all the component factors of the state
Identify all the allowable values for each factor
The number of states is the product of the number of allowable values of all the factors
Impossible States:
Certain combinations of factors might appear to be impossible
Example: A broken engine cannot run. So, combination fo factors for transmission and engine condition will be 3 and not 4. Hence, total number of states i s 108
Equivalent State:
Two states are sais to be "equivalent" if every sequence of inputs starting from one state generates the same sequence of outputs when started from the other state
Bugs arise with the improper merging of equivalent states
The reason for two states or two sets of states to appear equivalent is that the programmer has failed to give a proof of equivalence for every input sequence
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