Precalculated modified preorder tree traversal

MPTT it quite old and very clever way for transposing hierarchical - tree structure to a two-dimensional representation that is suitable for relational databases. MPTT allows to translate information about node tree position into two numbers - left and right bound. Two number fields can be easily indexed and look ups for records in the tree can take advantage of database indexes and perform really quickly. I won’t go into details of the (well) documented MPTT algorithm itself, because there are a lot of sources where you can go for comprehensible explanation (better than I would be able to provide).