| 摘要 |
A database management system includes a first data storage structure for storing timestamped counter data entries for each of devices in an unordered manner and such that each counter data entry is assigned a uniquely identifiable storage address; a second data storage structure for storing and mapping between: address data identifying the storage addresses of counter data entries, excluding those which are null or empty, timestamps corresponding to the counter data entries, and device identifiers identifying the devices to which the counter data entries correspond; and data access means for, in response to receiving a request for data in respect of a specified time period and at least one of the devices, using the second data storage structure to identify, for the or each specified device, the storage addresses of the temporally first and last counter data entries falling within the specified time period and not null or empty.
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