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j5's EventStream module provides an interface for exchanging data with services such as Tango and OPC. j5 models this data as a series of events. Each combines information on the source of the data, its reliability, when it was generated and whether it represents an alarm condition, with the actual data from the external device. Adding a new type of data source requires only the implementing of the very modest data device API. For Tango, the implementation built on PyTango while for OPC Windows COM was used. Data devices support both pulling values and subscription to event channels. Once in j5, events may flow through event pipes, being transformed and triggering actions such as the addition of logbook entries. In other cases, j5 may pull events from the data server, e.g. to populate data fields automatically when new log entries are created. A key feature enabled by EventStream is the ability to attach graphs of 1D and 2D arrays directly to logbook entries as they are added. This combines the event processing capabilities of j5 with its document attachment and thumbnail generation to make the information present in such arrays immediately available to logbook users.
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