4. The continuous query result estimator according to claim 2 , wherein the control module is configured to trigger the classification of the received set of data items by the classification module when one of a number and a proportion of expected data values determined to be missing from the received set of data items is one of at and below a threshold value.
2. The continuous query result estimator according to claim 1 , further comprising: a control module configured to: detect an absence of at least one expected data value in the received set of data items; and upon detecting an absence of at least one expected data value in the received set of data items, trigger the classification of the received set of data items by the classification module.