Transitive Dependency:
Definition and Explanation:
A functional dependency between two or more
non-key attributes in a relation is called transitive dependency. Suppose a
STUDENT relation with sample data is given below.
STUDENT (StdID, Name, Major, Advisor)
| StdID |
Name |
Major |
Advisor |
| MS-100 |
M |
Math |
Prof. B |
| MS-200 |
B |
Chemistry |
Prof. R |
| MS-300 |
A |
Physics |
Prof. T |
|
Figure 7.11: 'STUDENT' Relation |
The above relation is in second normal form
because primary key consists of only one attribute. The functional dependency
exists in this relation such as;
StdID →
Name, Major, Advisor
Suppose each major has exactly one advisor. In
this case, 'Advisor' is functionally dependent on 'Major' such as;
Major →
Advisor
So the transitive dependency exists in the above
relation because there is functional dependency between non-key attributes
'Advisor" and 'Major'.
Multi-Valued Dependency:
Multi-valued dependency exists when there are at
least three attributes in a relation. Suppose a relation R with attributes A, B
and C, There is a multi-valued dependency of attributes B and C on attribute A
if and only if the set of values of B and set of values of C associated with a
given value of A, but the set of values of B is independent of set C. The
multi-valued dependency is indicated by double arrows such as;
if A → B,
then A →
C
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