If a secondary index points to a dependent segment, the effect is to restructure the hierarchy so that the dependent segment appears as the root. In the new hierarchy, the higher level segments in the original hierarchy become dependents of the new root. They appear as leftmost dependents in reverse hierarchical order. A secondary index is similar to a logical relationship in that they both restructure an underlying hierarchy. However, a secondary index is different from a logical relationship in that it can deal only with a single physical database. Logical relationships can combine segments from one or more physical databases.
The diagram below illustrates an original, underlying hierarchy and the new hierarchy that results from indexing a dependent segment (SEG2).
Figure 16. Hierarchical restructuring via a secondary index
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