# Package org.eclipse.viatra.query.runtime.rete.aggregation

- Interface Summary
  Interface | Description
  --- | ---
  IAggregatorNode | Expresses that aggregators expose specialized non-enumerable indexers for outer joining.

- Class Summary
  Class | Description
  --- | ---
  ColumnAggregatorNode<Domain,Accumulator,AggregateResult> | Groups incoming tuples by the given mask, and aggregates values at a specific index in each group.
  CountNode | An aggregation node that simply counts the number of tuples conforming to the signature.
  IndexerBasedAggregatorNode | A special node depending on a projection indexer to aggregate tuple groups with the same projection.