Advances, Systems and Applications
Table 1 Retrieval and addition performances on primary/partial/full index models generated using the six key selection methods under different parameter distributions
Performance on primary index model | Original key | Random key | Minimun Key count | Maximum key count | Designated key | Least-used key |
 Retrieval  Equal parameter appearing probability | Averagea | Average | Average | Average | Average | Average |
 Retrieval  Unequal appearing probability of service input parameters | Average | Average | Average | Average | Average | Average |
 Retrieval  Unequal appearing probability of service retrieval request parameters | Good (453.9 ms) | Good (428.4 ms) | Fair (742.7 ms) | Fair (763.7 ms) | Good (392.0 ms) | Excellent (72.7 ms) |
 Addition  Equal parameter appearing probability | Average | Average | Average | Average | Average | Average |
 Addition  Unequal appearing probability of service input parameters | Average | Average | Average | Average | Average | Average |
 Addition  Unequal appearing probability of service retrieval request parameters | Average | Average | Average | Average | Average | Average |
Performance on partial/full index model | Original key | Random key | Minimum Key count | Maximum key count | Designated key | Least-used key |
 Retrieval  Equal parameter appearing probability | Average | Average | Average | Average | Average | Average |
 Retrieval  Unequal appearing probability of service input parameters | Average | Average | Average | Average | Average | Average |
 Retrieval  Unequal appearing probability of service retrieval request parameters | Good (485.1 ms) | Good (533.3 ms) | Fair (765.2 ms) | Fair (807.7 ms) | Good (482.9 ms) | Excellent (84.2 ms) |
 Addition  Equal parameter appearing probability | Fair (4696.4 ms) | Fair (4607.9 ms) | Fair (4698.9 ms) | Fair (4828.9 ms) | Excellent (1122.2 ms) | Good (2626.9 ms) |
 Addition  Unequal appearing probability of service input parameters | Fair (7262.5 ms) | Fair (6264.5 ms) | Fair (7771.1 ms) | Fair (7694.0 ms) | Excellent (1271.6 ms) | Good (1606.5 ms) |
 Addition  Unequal appearing probability of service retrieval request parameters | Fair (4740.5 ms) | Fair (4887.0 ms) | Fair (4339.6 ms) | Fair (4652.4 ms) | Excellent (1170.4 ms) | Good (2567.6 ms) |