Disclosed is an event correlation detection system that can automatically set a minimum supporting rate and a minimum reliability rate so that an erroneous detection rate is reduced to an allowable level. The event correlation detection system 101 includes an arrival rate calculation unit 102 calculating an arrival rate, an occurrence probability calculation unit 103 calculating a first probability, a threshold calculation unit 104 calculating the minimum supporting rate and the minimum reliability rate for a dependency rule, and an event association rule engine unit 160 detecting an association among a plurality of event types.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. An event correlation detection system that comprising, for a plurality of event types: an arrival rate calculation unit that calculates, for each of the event types, an arrival rate that the event type arrives during a predetermined time period; an occurrence probability calculation unit that calculates, for each of the event types, a first probability that the event type occurs, based on the arrival rate and the predetermined time period; a threshold calculation unit that calculates a second probability that the plurality of event types occur, based on the first probability, and calculates a minimum supporting rate for a combination of event types and a minimum reliability rate for a dependency rule, based on the second probability; and an event association rule engine unit that detects an association among the plurality of event types in accordance with the minimum supporting rate and the minimum reliability rate. 2. The event correlation detection system according to claim 1 further comprising a window division unit that classifies the event types in the respective predetermined time period, associating the respective predetermined time period with a set of the classified event types, and generates a window, wherein the arrival rate calculation unit performs calculation in accordance with the window. 3. The event correlation detection system according to claim 2, further comprising a combination generation unit that generates a group of the plurality of event types residing in the window, gathers the groups, and thereby generates a first combination; a combination selection unit that calculates a supporting rate indicating a ratio of a number of the windows in which all the event types residing in the group pertaining to the first combination appear, to a number of all the windows, and selecting, among the first combination, the specific group for which the supporting rate takes a value larger than the minimum supporting rate, as a second combination; a dependency rule generation unit that generates a dependency rule that includes a consequent, corresponding to one event type among event types in a group residing in the second combination, and an antecedent, corresponding to remaining event types; and a dependency rule selection unit that calculates a reliability rate indicating a ratio of a number of windows in which the event types appearing in the dependency rule appear, to a number of the windows in which the antecedent appears, wherein the event association rule engine unit detects an association among the event types based on magnitude of the reliability rate and the minimum reliability rate. 4. The event correlation detection system according to claim 3, wherein the combination generation unit specifies a combination number to be two; the combination generation unit performs a first process for generating the group by combining the combination number of the event types; the event association rule engine unit performs a second process for retaining the second combination as a third combination when deciding that there exists a group for which the reliability rate is larger than the minimum reliability rate, and then performs a third process for increasing the combination number by one; the event association rule engine unit repeats the first to third processes in sequence until deciding that there exists no group for which the reliability rate is larger than the minimum reliability rate; and the event association rule engine unit outputs the specific third combination last retained by the event association rule engine unit, when deciding that there exists no group for which the reliability rate is larger than the minimum reliability rate. 5. The event correlation detection system according to claim 2, wherein the threshold calculation unit includes: a probability distribution calculation unit that calculates the second probability based on the first probability, gathers calculated values, and thereby generates a probability distribution G(i) (where i is a natural number); and a distribution probability calculation unit that obtains, in the probability distribution G(i), a total sum of G(i) for a value of i equal to or larger than a specific value, and outputs the specific value that is a lowest within a range in which a product of the obtained total sum and the total number of windows is equal to or lower than a predetermined assumed erroneous detection rate. 6. The event correlation detection system according to claim 2, wherein the threshold calculation unit calculates Pr(|E|>0|W) representing the first probability in accordance with a process of Pr(|E|>0|W)=1−exp(−E×W) (where W is a time period in the window, E=NE÷T, exp( ) is an exponential function, T is a time period, NE is a number of times of occurrence of an event type E during a time period T, |E| is a number of times of occurrence of events having an event type E, and Pr(|E|>0|W) is a probability of occurrence of events having an event type E during a time period W in the window); calculates the second probability based on the first probability; and calculates the minimum supporting rate based on the second probability. 7. The event correlation detection system according to claim 2, wherein the threshold calculation unit calculates Pr(R|W) representing the first probability in accordance with a process of Pr(R|W)=Pr(|A|>0|W) (where R is a dependency rule, A is the consequent in the dependency rule, W is a time period in the window, |A| is a number of times of occurrence of events having an event type A, Pr(|A|>0|W) is a probability of occurrence of at least one event having an event type A during a time period W in the window, and Pr(R|W) is a probability of “occurrence of a dependency rule R during a time period W in the window”); calculates the second probability based on the first probability; and calculates the minimum reliability rate based on the second probability. 8. The event correlation detection system according to claim 5, wherein the threshold calculation unit calculates the probability distribution in accordance with calculation processing of a binomial distribution with the number of time periods existing in the window and the first probability, and calculates the minimum supporting rate based on the probability distribution. 9. An event correlation detection method comprising, for a plurality of event types: calculating, for each of the event types, an arrival rate that the event type arrives during a predetermined time period; calculating, for each of the event types, a first probability that the event type occurs, based on the arrival rate and the time period; calculating a second probability that the plurality of event types occur, based on the first probability and calculating a minimum supporting rate for an event type combination and a minimum reliability rate for a dependency rule, based on the second probability; and detecting an association among the plurality of event types in accordance with the minimum supporting rate and the minimum reliability rate. 10. A non-transitory computer readable media storing, a computer program causing a computer to implement functions comprising, for a plurality of event types: an arrival rate function that calculates, for each of the event types, an arrival rate that the event type arrives during a predetermined time period; an occurrence probability calculation function that calculates, for each of the event types, a first probability that the event type occurs based on the arrival rate and the time period; a threshold calculation function that calculates a second probability that the plurality of event types occur, based on the first probability, and calculating a minimum supporting rate for an event type combination and a minimum reliability rate for a dependency rule, based on the second probability; and an event association rule engine function that detects an association among the plurality of event types in accordance with the minimum supporting rate and the minimum reliability rate. 11. The event correlation detection system according to claim 5, wherein the threshold calculation unit calculates the probability distribution in accordance with calculation processing of a binomial distribution with the number of time periods existing in the window and the first probability, and calculates the minimum reliability rate based on the probability distribution. 12. The event correlation detection system according to claim 5, wherein the threshold calculation unit calculates a lowest s satisfying (Σi>s_Nw×G(i))<p0 (where Nw is a total number of the windows, G(i) is the probability distribution calculated based on the E, (Σi>s_Nw×G(i)) is a total sum of Nw×G(i) for i larger than t, p0 is the assumed erroneous detection rate, and i is a natural number); and specifies the calculated value as the minimum supporting rate. 13. The event correlation detection system according to claim 5, wherein the threshold calculation unit calculates a lowest t satisfying (·i>t_Nw×dR(Nw, W, R)(i))<p0 (where Nw is a total number of the windows, dR(Nw, W, R)(i) is the probability distribution calculated based on the dependency rule R, (Σi>t_Nw×dR(Nw, W, R)(i)) is a total sum of Nw×dR(Nw, W, R)(i) for i larger than t, p0 is the assumed erroneous detection rate, and i is a natural number); and specifies the calculated value as the minimum reliability rate.