Discuss how the definitions of 2NF and 3NF based on primary keys differ from the general definitions of 2NF and 3NF. Provide an example to illustrate your answer.
What will be an ideal response?
The above definitions for second (2NF) and third normal form (3NF) disallow partial or
transitive dependencies on the primary key of relations to avoid update anomalies. However,
these definitions do not take into account other candidate keys of a relation, if any exist. The
more general definitions for 2NF and 3NF take account of the candidate keys of a relation.
Note that this requirement does not alter the definition for 1NF as this normal form is
independent of keys and functional dependencies. For the general definitions, we define
that a primary-key attribute is part of any candidate key and that partial, full, and transitive
dependencies are with respect to all candidate keys of a relation.
Second normal form (2NF) A relation that is in First Normal Form and every non-
candidate-key attribute is fully functionally dependent on any candidate key.
Third normal form (3NF) A relation that is in First and Second Normal Form and in
which no non-candidate-key attribute is transitively dependent on any candidate key.
When using the general definitions of 2NF and 3NF we must be aware of partial and transitive
dependencies on all candidate keys and not just the primary key. This can make the process of
normalization more complex, however the general definitions place additional constraints on
the relations and may identify hidden redundancy in relations that could be missed.
You might also like to view...
Write a statement that inputs the values for the elements of t from the keyboard.
What will be an ideal response?
Of the following statements, which is the best comparison of repeaters and bridges?
A. Repeaters and bridges both amplify the data and retransmit the frames to provide better fault tolerance. B. A repeater is an intelligent device that examines the packets while a bridge merely links segments C. Repeaters retransmit all packets, while bridges examine the destination MAC address to determine which packets to forward onto the next segment. D. While bridges link segments to make a larger network, repeaters help manage and reduce traffic
When Excel draws a(n) _________________________ chart, it always positions the chart so that one of the dividing lines between two slices is a straight line pointing to 12 o'clock (or 0 degrees).
Fill in the blank(s) with the appropriate word(s).
____________________ have many of the same properties as layers.
Fill in the blank(s) with the appropriate word(s).