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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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Could someone please give me an example of a 3NF *DECOMPOSITION* that is not in BCNF? (I have no problem determining this for non-decompositions.)

It seems to me that Bernstein's synthesis / 3NF synthesis always yields BCNF subrelations, but that's apparently not true. When one uses 3NF synthesis, one will have subrelations as a result, and they will each consist of either: just one…
Alfred Kaminski
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Using 3NF in Laravel's ORM

I am trying to build a simple Laravel application. My data model looks like the following: ENTITIES: Project, Requirements, ProjectRequirementStatus RELATIONSHIPS: A Project has many Requirements A requirement belongs to many Projects as a…
Neurax
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Normalization to 3NF

Is the following table in 3NF: Customer(CustomerID, CustomerName, DOB, Phone, Address) I am specially interested to know if the address field should be in this table or should it be further decomposed.
Swaranga Sarma
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Are both definitions to 3NF equal?

From 3rd Normal Form Definition: A database is in third normal form if it satisfies the following conditions: It is in second normal form. There is no transitive functional dependency. By transitive functional dependency, we mean we have the…
Stav Alfi
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What is the correct approach when decomposing dependencies

I am struggling with Carnonical Cover, Dependency Preservation and Lossless Decomposition. Are the approach and thoughts here correct? R(ABCDEFG) Provided is the following set of dependencies after a canonical cover has been made. I did not do the…
Paludan
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3NF Normalization Algorithm Step: Relation with SuperKey

I was wondering about the last step of the 3NF normalization algorithm where it states: 4) If none of the relations obtained in previous steps contains a superkey of R, then add a new relation whose schema is a key for R. My specific question is,…
John
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How to identify the corrects step to complete 3NF?

This is an example from a textbook: Consider the relation R (A ,B ,C ,D ,E ) with FD’s AB -> C, C -> B, and A -> D. We get that the key is ABE and ACE. With decompositions: ABE+=ACE+=ABCDE. How do you check minimality? I know that AB+=ABD and the…
mamajava
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A fatal JavaScript error?

I am trying to figure how to fix this error I keep receiving when I am applying Normalization to my tables in phpMyAdmin. This only pops up at the bottom of the screen when ever I try to complete the 3NF of the normalization process. Below is a…
The ONLY One
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determining foreign, primary keys, 1nf, 2nf, 3nf given table and functional dependencies

first and foremost i would like to say that this is for a past homework assignment that i could not figure out and have come here to ask for clarification. I am having trouble with normalization for this specific question.…
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3NF and lossless decomposition of relation and functional dependencies

I am trying to find the 3NF lossless decomposition of the following relation with respect to the functional dependencies: I started by deriving the keys from the functional dependencies given above. The keys are {L,T}, {E,T} and {T,M} because all…
bawse
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Is it still normalized db schema? database

I have the following db-schema . FILE, GROUP and BLOCK represent the object structure of the XML file. FILE is the root. GROUP has FK to FILE. BLOCK has the one FK to GROUP and the another one FK to UNIT. UNIT groups "similar" BLOCKs from…
dpolaczanski
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Creating Functional Dependencies and identifying Normal Forms from ER Diagram

I am an ICS student and I have been given two questions. 1.) List all the Functional Dependencies that hold for the database. 2.) For each relation in your relational schema write down whether the relation is in BCNF or 3NF and if not give a…
Jarrod Lofy
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Can someone tell me if this relation is in 3NF?

Consider a relation R(A, B, C, D, E) with the following function dependencies: A->BC, D->CE, C->E AD+ = ABCDE Prime Attributes: AD Non-Prime Attributes: BCE Decomposed into 3NF but not BCNF R1(A, B, C, D) R2(C,E)
Cillian Hughes
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SQL - entity relationship diagram

I have to create an entity relationship diagram for an SQL database. This question relates to a previous question I posted: Normalisation - SQL - 3NF I have done the following entity relationship diagram and was wondering if it is correct (such as…
R. Jones
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How can I achieve 3NF with a database that has multiple date fields and two different users?

I hope to reach 3NF with my database that is not particularly well made but functions ok...My main concern is whether there is a need for perfect 3NF, if there is such a thing, and if I should make adjustments on any of the tables to get to a good…
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