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Why is it important that relations in a database are in 3NF?
As you already know, it reduces the duplication of data in a table(relation) but it keeps the referential integrity – the information is the same but presumably more optimized. It has a cost though – more tables, related with foreign key relationship. This usually adds abstraction on the database.
Can a relation be in 3NF but not in 2NF?
Yes, Korth’s definition for 3NF implies 2NF. The candidate key here is {pub_id, auth_id} . Obviously, this relation is not in 2NF because publisher_name is dependent on pub_id , which is a subset of the candidate key (therefore it is not fully functionally dependent on the only candidate key).
Is this relation in BCNF?
A relation is in BCNF iff, X is superkey for every functional dependency (FD) X? Y in given relation. In other words, A relation is in BCNF, if and only if, every determinant is a Form (BCNF) candidate key.
Is a relation in 3NF also in BCNF?
Every relation in BCNF is also in 3NF, but the reverse is not necessarily true. 3NF allows attributes to be part of a candidate key that is not the primary key; BCNF does not. This means that relations in 3NF are often in BCNF, but not always. the keys overlap, that is, some attributes in the keys are common.
Are relation is in 2NF if?
A relation is in 2NF if it has No Partial Dependency, i.e., no non-prime attribute (attributes which are not part of any candidate key) is dependent on any proper subset of any candidate key of the table.
When is a relation in a 3NF form?
A relation is in 3NF if at least one of the following condition holds in every non-trivial function dependency X –> Y: X is a super key. Y is a prime attribute (each element of Y is part of some candidate key).
What is the purpose of going to 3NF?
The purpose of going to 3NF is that on this normal form, we will eliminate functional dependencies on non-key fields. At this stage, all non-key fields are dependent only on the key.
When to use third normal form ( 3NF )?
X is a super key. Y is a prime attribute (each element of Y is part of some candidate key). A relation that is in First and Second Normal Form and in which no non-primary-key attribute is transitively dependent on the primary key, then it is in Third Normal Form (3NF). Note – If A->B and B->C are two FDs then A->C is called transitive dependency.
When is a relation in third normal form?
A relation is in third normal form, if there is no transitive dependency for non-prime attributes as well as it is in second normal form. A relation is in 3NF if at least one of the following condition holds in every non-trivial function dependency X –> Y: X is a super key. Y is a prime attribute (each element of Y is part of some candidate key).