A method for choosing a data source out of a plurality of data sources by a computer backend machine of a computer network, the plurality of data sources comprising - an inventory source which reflects an actual status of bookings made for travel products, - a base availability source which is a simplified version of the inventory source and stores availability information periodically updated from the inventory source, - an availability cache source which is fed with results obtained from past availability requests, the method comprising: - providing a target value of a statistical indicator to the computer backend machine, the statistical indicator being a polling error rate of the inventory source which represents a ratio between a number of access failures and a number of access attempts to the inventory source; - associating to the computer backend machine at least a first decision rule for selecting one out of the plurality of data sources, the first decision rule defining a decision to which data source a request is directed, the decision rule being based on a current order value which is a numerical value between 0% and 100% and defines an access attempt rate to the inventory source; - periodically observing a current value of the statistical indicator by an observer associated to the computer backend machine; - dynamically re-computing the first decision rule upon detection that the observed current value of the statistical indicator differs from the target value of the statistical indicator comprising calculating an updated order value by ∘ increasing the current order value if the current value of the statistical indicator is smaller than the target value of the statistical indicator, ∘ decreasing the current order value of the statistical indicator if the current value is bigger than the target value of the statistical indicator, wherein the updated order value is calculated by applying an exponential response function based on at least the current order value, the target value of the statistical indicator and the current value of the statistical indicator. - an inventory source which reflects an actual status of bookings made for travel products, - a base availability source which is a simplified version of the inventory source and stores availability information periodically updated from the inventory source, - an availability cache source which is fed with results obtained from past availability requests, - providing a target value of a statistical indicator to the computer backend machine, the statistical indicator being a polling error rate of the inventory source which represents a ratio between a number of access failures and a number of access attempts to the inventory source; - associating to the computer backend machine at least a first decision rule for selecting one out of the plurality of data sources, the first decision rule defining a decision to which data source a request is directed, the decision rule being based on a current order value which is a numerical value between 0% and 100% and defines an access attempt rate to the inventory source; - periodically observing a current value of the statistical indicator by an observer associated to the computer backend machine; - dynamically re-computing the first decision rule upon detection that the observed current value of the statistical indicator differs from the target value of the statistical indicator comprising calculating an updated order value by ∘ increasing the current order value if the current value of the statistical indicator is smaller than the target value of the statistical indicator, ∘ decreasing the current order value of the statistical indicator if the current value is bigger than the target value of the statistical indicator, wherein the updated order value is calculated by applying an exponential response function based on at least the current order value, the target value of the statistical indicator and the current value of the statistical indicator. ∘ increasing the current order value if the current value of the statistical indicator is smaller than the target value of the statistical indicator, ∘ decreasing the current order value of the statistical indicator if the current value is bigger than the target value of the statistical indicator, wherein the updated order value is calculated by applying an exponential response function based on at least the current order value, the target value of the statistical indicator and the current value of the statistical indicator.