The Nested Relational Database Model

Abstract

Up to this point, we have been dealing with the standard relational model introduced by Codd. Probably, one of the most fundamental assumptions made in this model is that data is represented in the form of flat tables; this is the so called first normal form assumption. In many practical circumstances, however, data is not represented as flat tables but rather in the form of hierarchically organized tables. For example consider the table shown in Figure 7.1. A row in that table represents a person, the set of his or her natural children and for each child, the set of his or her toys. In the relational model this table would be represented as shown in Figure 7.2. The argument made by many people is that the hierarchically organized table is a more natural representation of this data. So there is a need to represent and manipulate such data.