The foglamp-rule-periodic plugin is a notification rule that is used to trigger at regular intervals when data is being received for an asset.
Asset: the single asset that the plugin should monitor.
Interval: the minimum time interval, in seconds between the rule triggering.
Whenever the plugin receives data for the specified it will check to see how long it has been since it last triggered. If it is interval seconds or longer since it triggered then the rule will be triggered. If no data is being received for the specified asset then the rule will not trigger.
This rule is commonly used to perform periodic operations, such as data sampling on an asset, the action associated with the rule could be to enable and disable an instance of the foglamp-filter-asset to control sending this data to the north.
A similar rule, foglamp-rule-watchdog exists that will trigger if data is not seen for a given asset within a given time frame.