Database Reference
In-Depth Information
Corollary of Heath's Theorem
An important corollary from Heath's theorem is as follows:
Example 3:
The following example illustrates the importance of the
above-mentioned corollary:
Conclusion
Based on Heath's theorem and its corollary, we can assert with confidence, the following
advice:
•
Decompose only when there is a non-loss decomposition such
that the resulting relations do not share a candidate key.
•
Do not decompose if each resulting relation does not have a
primary key.
4.5 The First Normal Form
By definition, all relations are in 1NF. This is by no means coincidental, but by
design: we defined a relation to consist of atomic attributes, and subject to the entity
integrity constraint and the referential integrity constraint. However, as you will soon see,
having relations in 1NF only is often not good enough.
