User talk:76.10.149.6

FK for hierarchical mapping doesn't work
The section:

In this, the "child" is the same type as the "parent". The hierarchy stating EmpNo 10 is boss of 20, and 30 and 40 each report to 20 is represented by the "ReportsTo" column. In Relational database terms, the ReportsTo column is a foreign key referencing the EmpNo column.

doesn't work because the Director has no "ReportsTo" and so the FK constraint prevents the addition of this tuple in the relation. You could have the director report to himself (i.e., set it to 10) but this still has the problem that the relational model has a link in it that is not a root as occurs in the hierarchical model. Further, nothing forces the links up the chain; this relation doesn't force a tree model.