Database Reference
In-Depth Information
Figure 1.10
Third Normal
Form (3NF).
to popular belief, SQL code joins are never tunable in comparison to
simple SELECT statements against a single table.
Fourth Normal Form (4NF)
. Now the concept of Normal Forms
gets even grayer, or perhaps just fuzzier. 4NF entities are often created
in order to remove potentially null-valued columns into separate enti-
ties, minimizing physical space. Because Oracle Database tables use
variable-length records, there is really no point in separating nulls
into separate entities because null is nothing anyway. Nothing occu-
pies no space whatsoever, and thus 4NF is even grayer than 3NF, or
as I said just fuzzy!
Fifth Normal Form (5NF) and Beyond
. As far as performance is
concerned, 5NF and beyond should simply be avoided. In fact, 3NF
and beyond are often commercially unviable, usually totally impracti-
cal, and nearly always detrimental to performance.
1.2.1.1
Referential Integrity
2
Referential Integrity
is a mechanism used to validate data between primary
and foreign key columns in related tables. In order to explain Referential
Integrity briefly, we need to backtrack a little to both data modeling evolu-
tion and Normalization.
