Frame register(RelNode rel, RelNode newRel,
                 Map<Integer, Integer> oldToNewOutputs,
                 SortedMap<CorDef, Integer> corDefOutputs) {
    final Frame frame = new Frame(rel, newRel, corDefOutputs, oldToNewOutputs);
    map.put(rel, frame);
    return frame;
  }
Registers a relational expression and the relational expression it became
after decorrelation.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java