Linearized Tree Model
Just as "Nested Set Model" has a sibling model "Nested Intervals Model" that changed left-right columns to float, FF model has sibling model such as it. It is "Linearized Tree Model" that changed QUEUE column to float. If QUEUE is real, can divide indefinitely. And cost at the time of adding nodes can be reduced.
"Linearized Tree Model" is established on the theory. However, when to use practically, occur the problem that I had known already it. The rationale is also the same as the nested set model, since it is finite SQL real accuracy, it was that not separate them indefinitely.