In GeoEvent Server, every GeoEvent has an associated set of properties such as the GeoEvent Definition used to construct the GeoEvent. Recall that a GeoEvent Definition is the 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 Field parameter displays a list of field names from available GeoEvent Definitions. At the top of this list are several GeoEvent Server properties including the following:
Constructing a filter with the expression $DEFINITION_NAME = Flights-TcpTextIn would discard any GeoEvents that do not contain the Flights-TcpTextIn GeoEvent Definition name. A filter such as this one, that is based on a GeoEvent Definition property, can be used to filter any GeoEvents that do not adhere to a required schema.