This module includes Plan Nodes below.

--- L-node ---
who has only left child

[SCAN node] - Scan node
[GCNT node] - Get Count node
[VIEW node] - View node ( Scattered tuple -> physical one tuple-row )

--- B-node ---
who has left child and any expression

[PROJ node] - Projection node
[FILT node] - Filter node
[QSRT node] - Quick Sort node
[HASH node] - Hash node
[GRAG node] - Group Aggregation node
[GRBY node] - Group By node
[AGGR node] - Aggregation node

--- R-node ---
who has left child and right child

[JOIN node] - Join node
[SUNI node] - Set Union node
[BUNI node] - Bag Union node
[SITS node] - Set Intersect node
[SMIN node] - Set Minus(Difference) node
[CONC node] - Concatenation node

--- T-node ---
who has left child and right child and any expression

[LOJN node] - Left Outer Join node
[FOJN node] - Full Outer Join node
[AOJN node] - Anti Left Outer Join node
