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In FMv2, a EVENT is created when the temperature is outside set limits or out of bound i.e. the temperature is too low or too high. When the temperature logger sense that the temperature is outside set limits, the system creates an EVENT to identify abnormal temperature. The EVENT is ON-GOING or ACTIVE while the temperature is out of bound. 

What is "Aggregation"

"Aggregation" basically means "a group or mass of distinct or varied  things". things", In FMv2, it means that same type of Events are merged together into one Event. For example, if all loggers in a freezers measures too high temperature and all of them would activate an Event. In FMv2, these Events would merge into one Event. This is done to reduce the number of alerts that one can receive. 

What is "Propagation"?

When the system creates an Event, the Event can propagate up the entity tree. For example, we could have a person that is responsible for temperature monitoring in a one warehouse in one region. This person could subscribe to high severity temperature excursion at collection level. When one measuring point creates an High Temperature Event, the Event will travel up the entity tree , show the Event on the Collection level and send out alert to thous who has superscribed