The Nested Universal Relation Database Model

This monograph describes a method of data modelling whose
basic aim is to make databases easier to use by providing
them with logical data independence. To achieve this, the
nested UR (universal relation) model is defined by extending
the classical UR model to nested relations. Nested relations
generalize flat relations and allow hierarchically
structured objects to be modelled directly, whereas the
classical UR model allows the user to view the database as
if it were composed of a single flat relation. The author
presents a comprehensive formalisation of the nested
relational model, which incorporated null values into the
model. Functional data dependencies and the classical notion
of lossless decomposition are extended to nested relations
and an extended chase procedure is defined to test the
satisfaction of the data dependencies. The nested UR model
is defined, and the classical UR model is shown to be a
special case of the nested model.This implies that an UR
interface canbe implemented by using the nested UR model,
thus gaining the full advantages of nested relations over
flat relations.