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Questions tagged [bcnf]

Boyce–Codd normal form (or BCNF or 3.5NF) is a normal form used in database normalisation.

Boyce–Codd normal form (or BCNF or 3.5NF) is a normal form used in database normalisation. It is a slightly stronger version of the third normal form (3NF). BCNF was developed in 1974 by Raymond F. Boyce and Edgar F. Codd to address certain types of anomaly not dealt with by 3NF as originally defined.

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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…
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How is every binary relation BCNF?

So, as part of my assignment, I have to prove that any relation with two attributes is in BCNF. As per my understanding, if for a relation we have 3rd normal form and one non key attribute functionally determine key attribute, it violates the…
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Lossless, dependency preserving decomposition of a relation in 3rd Normal Form

I am learning about normalization of databases and I came across the following problem: Given the following relation, BOSQID and its functional dependencies F={S->D, I->B, IS->Q, B->O}, How would I go about finding a lossless, dependency…
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what is the benefit of the Fourth normal form?

I googled a lot, but I did not found an answer to that question. The first three normal forms are common sense. They are used to save consistency and avoid anamalies. But why do we need the BCNF and the fourth normal form? (the fifth I do not even…
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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…
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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…
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Database BCNF Violations

I am confused about a particular aspect of DB BCNF violation criteria. Here's an example: R(ABCDEF) The FDs are BC->D, C->AF, AB->CE. I have derived the candidate keys to be AB and BC. The relation is in BCNF right, given all of the FDs contain at…
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Checking if a decompozition is in Boyce Codd Normal Form

Consider the schema S=(A,B,C,D) having AB as primary key, and the following functional dependencies (FD) hold on it: AB --> C, AB --> D, BC --> D. Is the following decomposition in Boyce-Codd Normal Form (BCNF)? S1=(A,B,D) & S2=(B,C,D) Attempted…
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BCNF vs 3NF technical questions

There are many related questions on SO, but none that I can find that answer this question: Is it possible to have a 3NF relation that can be lossless-join decomposed into BCNF relations while preserving dependencies? I'm aware that you can…
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BCNF conversion algorithm

I'm learning the BCNF conversion algorithm and I'm not sure if I understood correctly of what happens when after you decompose the initial relation you still have a subscheme that is not in BCNF. For example: Given these Relation scheme and set of…
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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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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…
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Why is a non-dependency preserving BCNF decomposition still considered to be in BCNF?

From the Database Systems Concept textbook, for a schema r with the set of dependencies F to be considered in BCNF, for all dependencies in F+ (i.e. the closure of F) of the form a → b, at least one of the following must be true: a → b is a trivial…
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Does the relational schema with some "aggregation" attributes satisfy Boyce–Codd normal form (BCNF)?

Suppose a relational database has employee and company entity with workFor relation, such as employee(ssn, first_name, last_name), where ssn is the key. company(company_name, location), where company_name is the key. workFor(ssn, company_name),…
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