Every GeoEvent in GeoEvent Server has an associated set of properties such as the GeoEvent Definition used to construct the GeoEvent. Recall that a GeoEvent Definition is a schema that identifies the attribute fields and data types—date, string, integer, and so forth—for the GeoEvent's data. A filter can be configured to filter GeoEvents based on their properties such as their GeoEvent Definition.
When configuring a filter expression, the drop-down for the Field parameter displays a list of field names from available GeoEvent Definitions. At the top of this list are several GeoEvent Server properties including:
Constructing a filter with the following expression would discard any GeoEvents that do not contain the Flights-TcpTextIn GeoEvent Definition name: $DEFINITION_NAME = Flights-TcpTextIn. A filter like this one that is based on a GeoEvent Definition property could be used to filter any GeoEvents that do not adhere to a required schema.