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It does not have any non-prime attribute that is functionally dependent on any proper subset of any candidate key of the relation (i.e. it lacks partial dependencies). A non-prime attribute of a relation is an attribute that is not a part of any candidate key of the relation. Put simply, a relation (or table) is in 2NF if:
The columns in a candidate key are called prime attributes, [3] and a column that does not occur in any candidate key is called a non-prime attribute. Every relation without NULL values will have at least one candidate key: Since there cannot be duplicate rows, the set of all columns is a superkey, and if that is not minimal, some subset of ...
No non-prime attribute of R is transitively dependent on the primary key. A non-prime attribute of R is an attribute that does not belong to any candidate key of R. [3] A transitive dependency is a functional dependency in which X → Z (X determines Z) indirectly, by virtue of X → Y and Y → Z (where it is not the case that Y → X). [4]
Every non-trivial functional dependency either begins with a superkey or ends with a prime attribute (attributes depend only on candidate keys) [5] Every non-trivial functional dependency either begins with a superkey or ends with an elementary prime attribute (a stricter form of 3NF) —
In the Today's court bookings table, there are no non-prime attributes: that is, all attributes belong to some candidate key. Therefore, the table adheres to both 2NF and 3NF. The table does not adhere to BCNF. This is because of the dependency Rate type → Court in which the determining attribute is Rate type, on which Court depends.
In addition to this relationship, the table also has a functional dependency through a non-key attribute Department ID → Department Name; This example demonstrates that even though there exists a FD Employee ID → Department ID - the employee ID would not be a logical key for determination of the department Name.
B → C direct dependency relationship exists. Then the functional dependency A → C is a transitive dependency (which follows the axiom of transitivity ). In database normalization , one of the important features of third normal form is that it excludes certain types of transitive dependencies.
A key made from only one attribute. Concatenated A key made from more than one attribute joined together as a single key, such as part or whole name with a system generated number appended as often used for E-mail addresses. Compound: A key made from at least two attributes or simple keys, only simple keys exist in a compound key. Composite