Internal node with just a single child.
It does not directly contribute data to the result.
It must only result in tuples when the child does.
It can be joined with the child (P⋈C), or may, under some conditions, be omitted.
Internal node with multiple children.
It does not directly contribute data to the result.
It must only result in tuples when at least one of the children does.
This may be considered an inner join of the parent with the result of outer joining all children:
P⋈(⟗i=1n(Ci))
Returns the enum constant of this class with the specified name.
The string must match exactly an identifier used to declare an
enum constant in this class. (Extraneous whitespace characters are
not permitted.)
Parameters:
name - the name of the enum constant to be returned.