Hierarchies display data from tables or views in a graphical hierarchy. For example, you can create a hierarchy that displays an employee organization chart, or the hierarchical relationship between menus in a Web site.
The table or view on which the hierarchy is based must be self-referencing; that is, at least two columns in the table must share a recursive relationship. The SCOTT.EMP table has a recursive relationship between values in the MGR column and those in the EMPNO column. An employee's manager is shown in the table by the manager's employee number. To create a hierarchy based on this table, you identify to the build wizard MGR as a Foreign Key column and EMPNO as the Parent Key column.
The hierarchy can contain up to four levels. End users click links in the finished hierarchy to navigate up and down levels. For example, you can create an organization chart that allows end users to drill down to sales personnel and drill up to managers or farther up to vice presidents. As the end user drills up the hierarchy, new data from the table appear on the topmost or parent level.
You can add hypertext links to the hierarchy. For example, employee names in an organization chart could be hyperlinked to reports that provide additional information about the employee such as employee ID or salary.