Abstract: This disclosure relates to the processing of user events. In particular, it addresses various problems relating to the augmentation of a user event—received in a data stream of sequenced events—with data of one or more cooperating reference data items. For example, the augmented user events may be stored in an index on which queries can be run in real-time to extract aggregate and preferably anonymized information from those events according to the queries. Other example use-cases are also disclosed.