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Questions tagged [3nf]

Third normal form (3NF) is a database design principle originally defined by E.F. Codd in 1971. It is built on the First normal form (1NF) and Second normal form(2NF). A relation R is in third normal form if it is in second normal form and every non-prime attribute of R is non-transitively dependent on each candidate key of R.

3NF is a normal form used in database normalization originally defined by E.F. Codd in 1971. It is built on top of First normal form (1NF) and Second normal form (2NF). A table is in 3NF if and only if for each of its functional dependencies X → Y, at least one of the following conditions holds:

  • X contains Y (that is, X → Y is trivial functional dependency), or
  • X is a superkey, or
  • every attribute in Y-X, the set difference between Y and X is a prime attribute is contained within a candidate key.

In other words it states that all non-key attributes should be determined by the candidate keys and not by any non-key attributes.

Normalization beyond 3NF

Most 3NF tables are free of update, insertion of deletion anomalies. Certain types of 3NF are affected by such anomalies. Some tables fail short of Boyce-Codd normal form (BCNF) or higher normal forms like 4NF, 5NF or 6NF.

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Synthesis-algorithm for 3NF

I'm learning about databases and obviously I have to deal with normalforms. Now I came up with this very simple example; given a relation R with attributes {A, B, C} and functional dependencies {A,B -> C , A -> C}. The candidate key K for this…
TropicalSpore
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How to normalize these tables to 3NF

As part of a homework assignment I have been asked to create tables based on a case study, and all tables must be in 3NF. However, I've tried and tried to understand 3NF but I'm just not getting the hang of it and would appreciate some help. The…
h21
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Translating functional dependencies into 3rd normal form

I have this problem decomposing a relation schema into a set of schemas that are in 3NF. I have this relation schema: R= (A, B, C, D, E, F) With the following set F of functional dependencies: A → ABCDEF B → C D → E Can anyone help me out?
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3NF vs BCNF: Example

Gday lads, Ok, so I'm having a database class and I have this example that makes me think that I really didn't fully understand the difference between the two NFs.. I know that A relation, R, is in 3NF iff for every nontrivial FD (X->A)…
geekybedouin
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Can you move compound keys and/or foreign keys to other tables when normalizing to 3NF (third normal form)

My database design is currently at 3NF. The issue is foreign keys and in some cases compound keys. Can you move compound keys and/or foreign keys to create other tables provided the attributes associated with the compound/foreign keys do not rely on…
user1655231
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Trying to understand database normalization - 3NF

I am trying to understand database normalization, in particular 3NF. I am building a shop database and in trying to normalize to 3NF have come up with the structure below. The structure below assumes There may be multiple categories per…
someuser
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DB Tables which are in 3NF or 4NF but not in DKNF

Are there examples of Relational tables which are in 3NF or 4NF but not in Domain Key Normal Form?
simplfuzz
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Eliminating Transitive Functional Dependencies

(Primary keys in bold.) In one of my lectures, we took the following schema R(a, b, c, d, e) a -> b e -> b c, d -> a c, d -> b c, d -> e and took it to 2NF as follows: R1(c, d, a, e) c, d - > a and e R2(a, e, b) (Not in 2NF) a -> b e -> b …
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BCNF, 3NF, and candidate keys

I am having issues understanding how to determine if relations are in BCNF, 3NF, and in general identifying the candidate keys of a relation. Consider relation R = (A, B, C, D) with the functional dependencies: AB -> C C -> D D -> A The questions…
sudo_coffee
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BCNF Decomposition and Keys

I've been looking to decompose the following relation from its present state, into BCNF with three functional dependencies. Taking the maxim the key, the whole key, and nothing but the key I concluded that B-->C transitive functional dependency…
davidhood2
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How to decompose the schema into 3NF?

Schema R = (A,B,C,D,E) Functional Dependency F1 = {A->BC , CD->E, B->D, E->A} Functional Dependency F2 = {A->D, A->E, DE->BC, B->A, D->C} According to F1, candidate keys - A, E, BC, CD According to F2, candidate keys - A, B, DE Condition for a…
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Determining Super Key

According to Wikipedia Today's Court Bookings Each row in the table represents a court booking at a tennis club that has one hard court (Court 1) and one grass court (Court 2) A booking is defined by its Court and the period for which the Court…
q126y
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Table in 3rd normal form, yet with obvious redundancies

Assume the following Reservations table. Reservation_Number is the only candidate key: Reservation_Number Guest_Name ------------------ ------------ 1 john smith 2 john smith 3 john smith…
Jamshid
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Understanding BCNF Functional Dependency

I was following this tutorial for BCNF decomposition. The functional dependencies given are: A->BCD BC->AD D->B These are concerned with the relation R(A,B,C,D). The conditions for BCNF include: The relation must be in 3NF and when X->Y, X must be…
Java Enthusiast
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Third Normal Form in DBMS

I was just reading the definition of 3NF in DBMS, it states that: The functional dependency X --> A is allowed if: 1. X is a super key. 2. A is part of some key. I have 2 doubts: a: I don't get the point of how is the second condition useful to…
Maulik Soneji
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