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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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Simple Database normalization question

I have a quick question regarding a database that I am designing and making sure it is normalized... I have a customer table, with a primary key of customerId. It has a StatusCode column that has a code which reflects the customers account status…
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What is the importance of the 3nf

I've been given my assignment for college and one of the questions is to describe the importance of the 3NF. I understand normalisation is to eliminate data redundancy. Any help or resources would be of great help.
user4353777
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Table with unique identifier in Third normal form?

Suppose, I have a Table with the columns: person_id (primary key) first_name last_name birthday I also have a unique constraint on the combination {first_name, last_name} (I know that more people can have the same name, but I want to keep my…
physicalattraction
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Can you have a composite key when in Third Normal Form (3NF)?

I must normalise table data to 3NF. I have a composite key from 1NF, but all of the non-key attributes appear to be reliant on both of the primary key attributes. I'm trying to take it from 2NF into 3NF. Can I still have a composite key?
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Grails: Many-to-Many without hasMany/belongsTo - instead using native 3NF - Searching full text

I am implementing a many-to-many mapping in grails using 3NF, Not using the hasMany or belongsTo property. Taken from this article it shows and explains quite a lot about its advantages. Article: http://burtbeckwith.com/blog/?p=169 Presentation…
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Is a primary key on a many to many relation correctly normalised?

I have a many to many table (TableAB) which simply holds a foreign key to table A and a foreign key to table B. It always feels like I should also add a primary key column to the table itself, and that's what I'd normally do. But from an academic…
Ricky
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Understanding 3NF

I'm currently in a System Analysis class and I want to better understand the use of Normalization. For 3NF if I was working on a table that contained Student Id, Name, Phone Number, and Major. I would have to use only Student ID and Major because…
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BCNF/3NF in Relational Databases

How do you tell if a relation R is in BCNF and 3NF? I'm reading a textbook, and it's telling me that there are 3 main attributes you're looking at, but I'm having trouble understanding what they're saying, or at least applying what they're saying…
dxu
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Transitive dependence in Relational Database

I'm confused by the definition of transitive dependence in relational model of database. Codd's definition in his paper "Further normalization of the data base relational model" can be stated as follows: For three distinct collections A, B, C of…
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Data normalisation into third normal form

I have done data normalization on dummy data and would like to know if I did it correctly. If it is done correctly, I would also like to ask two things below, because it is about 3NF. 1NF: This table should be…
filtertips
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find all functional dependencies for attribute closure?

It is for a university assignment. I have to list all non-trivial functional dependencies that are applicable, while also trying to ensure that all tables in my schema are 3NF. I have created an ER Diagram & Relational Schema for my dataset. How can…
Iamclueless
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Higher normal form that this relation satisfies

Let R{A,B,C,D,E} be a relation with functional dependencies: B->EA EBC->D BED->A Question: What's the higher normal form that R satisfies? Attempt: 1NF: satisfied, since all the attributes are defined as single-valued. 2NF: I'm not exactly sure.…
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Does this 3NF decomposition have lossless join and is it also in BCNF?

I have this Relation and Functional Dependency: R = {A, B, C, D, E, G} FD = E->D C->B CBE->AG B->A G->E I tried to normalize using 3NF and got: After minimizing the FDs, I got E->D, C->B, CE->G, B->A, G->E So resulting…
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Normalization 3NF

I an reading through some examples of normalization, however I have come across one that I do not understand. The website the example is located here: http://cisnet.baruch.cuny.edu/holowczak/classes/3400/normalization/#allinone The part I do not…
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Does uniqueness of a non-key attribute violate 3NF?

As I was designing a database for my Database course, I came across a question that made me hesitant about my design. The exercise asked us about an arbitrary design that should be at least in 3NF. I am sure that the design is already in 1NF and…
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