Implement the underlying logical semantics only (identity function).
Naive cross node.
Naive cross node.
Naive equiJoin node.
Naive equiJoin node.
Fuse a groupBy and a subsequent fold into a single operator.
Operators added by backend-agnostic transformations.
Do not use those directly unless you want to hardcode physical execution aspects such as join order and caching and you know exactly what you are doing.