| 摘要 |
In a distributed system in which data is copied in response to a request of data from an operator, and the specifying of a data s ource, the information on identifying the version, and the validity time are recorded, a device on the data use side (1) checks t he validity time of the copy, provides the copy if the validity time has not expired yet, reads the latest data from a device holding the data source if the validity time has already expired, and makes a new copy and attribute information, (2) receives the instruction to alter the validity time of the copy held by the device, and (3) updates the validity of the corresponding copy according to the instruction; and a device on the data management side (4) records "the specifying of the data source, the information on identifying the version, and the validity time" of the data the validity time of which has been updated, and (5) takes out records of the data source indicated by the device on the data use side out of the records, and transmits the records taken out to the data use side requesting the data.
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