3. The continuous query result estimator according to claim 1 , further comprising: a control module configured to execute a first detection of an absence of at least one expected data value in the received set of data items, and a second detection of the absence of at least one expected data value in the received set of data items after a prescribed time interval from the first detection and, if at least expected data values are determined in the second detection to be missing, trigger the classification of the received set of data items by the classification module.
1. A continuous query result estimator for use in a data stream management system to reduce data stream processing times, the data stream management system being configured to execute a continuous query against data items received via at least one input data stream to generate at least one output data stream, the continuous query result estimator comprising: a classification module configured to classify a set of at least one data item received via the at least one input data stream into one of a plurality of input data groups; a data store configured to store, in association with each of the input data groups, a respective rule for estimating a result of executing the continuous query against a data item belonging to the input data group; and a result estimation module configured to: select a rule from the rules stored in the data store on the basis of the classification performed by the classification module; and apply the selected rule to the received set of data items to generate an estimate for a result of executing the continuous query against the received set of data items.