The implementation of the 'before' evaluator definition.
The before
evaluator correlates two events and matches when the temporal distance from the event being correlated to the current correlated belongs to the distance range declared for the operator.
Lets look at an example:
$eventA : EventA( this before[ 3m30s, 4m ] $eventB )
The previous pattern will match if and only if the temporal distance between the time when $eventA finished and the time when $eventB started is between ( 3 minutes and 30 seconds ) and ( 4 minutes ). In other words:
3m30s <= $eventB.startTimestamp - $eventA.endTimeStamp <= 4m
The temporal distance interval for the before
operator is optional:
NOTE: it is allowed to define negative distances for this operator. Example:
$eventA : EventA( this before[ -3m30s, -2m ] $eventB )
NOTE: if the initial value is greater than the finish value, the engine automatically reverse them, as there is no reason to have the initial value greater than the finish value. Example: the following two patterns are considered to have the same semantics:
$eventA : EventA( this before[ -3m30s, -2m ] $eventB ) $eventA : EventA( this before[ -2m, -3m30s ] $eventB )
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