Resolution:
This can be achieved by using the query engine as a pre-filter and implemented as described below in the Query and Inference agents.

In the query engine:

1.) Listen to your external events in a destination D1.
2). Upon reception of an event in D1:
    - Run the complex query.
    - If the query finds an existing concept, do nothing.
     - Else send the original event to the inference engine using a destination D2.

In the inference engine:

1). Listen to the events coming from the query engine through the destination D2.
2). Upon reception of an event in D2, always create the concept.