code: public void addObjectSink(final ObjectSink objectSink) {
          final ObjectTypeNode node = (ObjectTypeNode) objectSink;
          this.objectTypeNodes.put(node.getObjectType(),
                                   node);
      }
docs: Adds the <code>ObjectSink</code> so that it may receive
  <code>Objects</code> propagated from this <code>ObjectSource</code>.
  
  @param objectSink
  The <code>ObjectSink</code> to receive propagated
  <code>Objects</code>. Rete only accepts <code>ObjectTypeNode</code>s
  as parameters to this method, though.