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8.3 Hybrid Models > 8.3.3 Adjacency and Depth Model - Pg. 186

8.3 Hybrid Models 177 ('D', 3, 5, 6), ('E', 3, 7, 8), ('F', 3, 9, 10), ('G', 2, 12, 17), ('H', 3, 13, 14), ('I', 3, 15, 16); While the level number can be generated from the nested sets model in a VIEW, the query involves an expensive self-join. The advantage is in bill of materials ("B.O.M." or BOM) problems where subassembly data have to be computed up the tree from the leaf nodes (parts). 8.3.3 Adjacency and Depth Model This model adds a column for the depth of the node to the adjacency list, thus: CREATE TABLE Tree