This section describes the paths of the information going in and out of the Cascade Historian.
Input data points come from various external sources and supporting objects. This data is time stamped and placed into the current buffer in memory. Eventually the information is copied to the previous buffer and stored to the disk. This data transfer can be triggered by the following events:
As data accumulates on the disk, it can be transferred to an archive. Although the Cascade Historian itself does not provide this facility, it will detect and manage the files available to it. The data flow is summarized in the figure below:
Sources of commands for the Cascade Historian are various user's programs. The Cascade Historian responds to the following types of commands:
Control commands trigger certain actions in the Cascade Historian without requiring an answer (for example, register/de-register for a point, start/stop history). The Cascade Historian in turn may send a command to the Cascade DataHub (for example, to register for a point).
Requests for services, on the other hand, assume there will be an answer as output. The Cascade Historian allocates an answer buffer, where it places the required information. While proceeding with the service, the Cascade Historian may request information from the disk if the amount of data in the buffers is not sufficient to provide service.
The figure below illustrates command flow in the Cascade Historian.
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