Asynchronous Command Processing

This sequence of actions takes place once a received device Command is deemed to be asynchronous.

First, driver evaluates Event/Variable Update Qualifier Expression to figure out whether the Command is an Event (device-generated notification) or a Variable Update (delivery of device-side value change that contains new value). The qualified expression must return:

• 0 if the Command is an Event
• 1 if the Command is a Variable Update

If the Command is deemed an event, expressions in Asynchronous Event Processing group are evaluated:

• Event Name Expression must return name of Iotellect event.
• Event Timestamp Expression should return time when the event occurred in the device. By default, this expression is set to now(), what means that event's timestamp will be set to the time when it is constructed on the server.
• Event Level Expression must return level of Iotellect event. If is returns NULL, default level defined in Static Events table will be used.
• Event Data Expression must construct and return a Data Table representing event-specific data. Constructing a Data Table representing event data is normally performed by table() expression language function. The table() function should use event's format that can be retrieved via eventFormat() expression language function.

Once all the above expressions are evaluated, driver fires a new Iotellect Server event representing a device event. It's then stored and processed in a regular way.

If the Command is deemed a variable update, expressions in Asynchronous Variable Update Processing group are evaluated:

• Variable Name Expression must return name of the changed Iotellect variable.
• Variable Timestamp Expression must return device-side time when the change took place. By default, this expression is set to now(), what means that update's timestamp will be set to the time when it is processed on the server.
• Variable Quality Expression should return new variable value's quality or NULL if quality metric should be undefined.
• Variable Value Expression must construct and return a Data Table representing new variable's value. Constructing a Data Table representing variable value is normally performed by table() expression language function. The table() function should use variable's format that can be retrieved via variableFormat() expression language function.

Once all the above expressions are evaluated, driver registers a new update of Iotellect Server device variable. It's then stored and processed in a regular way.

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