| Interface | Description | 
|---|---|
| FilterFunction<M extends MessageEnvelope> | 
 A function that specifies whether a  
MessageEnvelope should be retained for further processing or filtered out. | 
| FlatMapFunction<M extends MessageEnvelope,OM extends MessageEnvelope> | 
 A function that transforms a  
MessageEnvelope into a collection of 0 or more MessageEnvelopes,
 possibly of a different type. | 
| JoinFunction<M extends MessageEnvelope,JM extends MessageEnvelope,RM extends MessageEnvelope> | 
 A function that joins  
MessageEnvelopes from two MessageStreams and produces
 a joined MessageEnvelope. | 
| MapFunction<M extends MessageEnvelope,OM extends MessageEnvelope> | 
 A function that transforms a  
MessageEnvelope into another MessageEnvelope, possibly of a different type. | 
| SinkFunction<M extends MessageEnvelope> | 
 A function that allows sending a  
MessageEnvelope to an output system. |