A computer-implemented reservation method and a corresponding system are utilized for controlling execution of a decision process to maintain data access efficiency upon receipt of a computation inquiry. The method comprises associating to a computer backend machine a configuration file containing at least a decision rule that drives the decision process and that is computed at least from a current value of a statistical indicator and a target value of the statistical indicator; periodically obtaining an up dated value of the statistical indicator; upon detection that the updated value is differing from the target value, dynamically updating the configuration file and storing in real-time a recomputed decision rule in the configuration file.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A method for choosing a data source out of a plurality of data sources having different accuracy levels by a computer backend machine of a computer network, comprising: providing a target value of a statistical indicator to the computer backend machine; associating to the computer backend machine at least a decision rule for selecting one out of the plurality of data sources; observing a current value of the statistical indicator by an observer associated to the computer backend machine; and dynamically re-computing the decision rule upon detection that the observed current value of the statistical indicator differs from the target value of the statistical indicator. 2. The method of claim 1, wherein the statistical indicator is one out of a polling error rate and a look-to-book number. 3. The method of claim 1 further comprising; generating an order value for the data source having the highest accuracy level depending on the detected difference between the current value of the statistical indicator and the target value of the statistical indicator. 4. The method of claim 3 further comprising: updating the order value when the detected difference indicates a change in the current value of the statistical indicator, wherein the updated order value is calculated depending on the previous order value and a history of order values. 5. The method of claim 1, wherein a first decision rule and a second decision rule are provided, wherein the first decision rule decides an access attempt rate for a first data source having the highest accuracy level out of the plurality of data sources and the second decision rule decides an access attempt rate for a second data source of a lower accuracy level out of the plurality of data sources when the first data source is not accessed. 6. The method of claim 1 further comprising: a decision process adapted to decide access to one out of the plurality of data sources upon receipt of a computational inquiry based on the decision rule. 7. The method of claim 6, wherein the decision process is a function of at least one characteristic of the computational inquiry. 8. The method of claim 1, wherein the plurality of data sources comprise at least one polling source selected among a dynamic availability polling source, a direct access polling source and an availability calculator source. 9. The method of claim 1, wherein the plurality of data sources comprise at least two out of a polling source, an availability status source (AVS) and an availability cache source. 10. The method of claim 1 further comprising: upon the updated value of the statistical indicator differing from the target value of the statistical indicator, computing an updated value of the order level based on the product of a current value of the order level with an exponential function of a difference between the target value of the statistical indicator and the updated value of the statistical indicator, and re-computing the decision rule so as to reach the updated value of the order level. 11. A computer program product stored in non-transitory computer-readable medium and comprising instructions adapted to perform the method of claim 1. 12. An availability inquiry system comprising at least one computer backend machine comprising: first memory adapted to store a target value of a statistical indicator; a second memory adapted to store at least a decision rule for selecting one out of a plurality of data sources having different accuracy levels; and an observer adapted to observe a current value of the statistical indicator, wherein the computer backend machine is configured to dynamically re-compute the decision rule upon detection that the observed current value of the statistical indicator differs from the target value of the statistical indicator. 13. The system of claim 12, wherein the statistical indicator is a polling error rate. 14. A reservation system comprising at least one computer backend machine, comprising: a first memory adapted to store a target value of a statistical indicator; a second memory adapted to store at least a decision rule for selecting one out of a plurality of data sources having different accuracy levels; and an observer adapted to observe a current value of the statistical indicator, wherein the computer backend machine is configured to dynamically re-compute the decision rule upon detection that the observed current value of the statistical indicator differs from the target value of the statistical indicator. 15. The system of claim 14, wherein the statistical indicator is a look-to-book ratio.