# Re: BCNF

Date: Sat, 2 Aug 2008 04:10:39 -0400

Message-ID: <jEUkk.17965$89.15424_at_nlpi069.nbdc.sbc.com>

<aarklon_at_gmail.com> wrote in message
news:3a1e04e9-e65f-469f-8357-f36486009e72_at_b38g2000prf.googlegroups.com...

*> Hi all,
**>
**> BCNF
**>
*

> the following is the definition is the definition of BCNF , which i

*> saw in a schaum series book
**>
**> 1) The relation is 1 N.F
**>
**> 2) for every functional dependency of the form X -> A , we have
**> either A C X or X is a super key of r. in other words,
**> every functional dependency is either a trivial dependency or in
**> the case that the functional dependency is not trivial then X must
**> be a super key.
**>
**> now my questions are as follows
**>
**> 1)
**>
**> we know that 2-ND normal form is all about separating partial
**> dependencies and full dependencies.third normal form is all about
**> removing transitive dependencies, in these lines can any one give
**> simple/ easy to understand method/explanation for converting a
**> relation in 3rd normal form to BCNF
**>
*

A relation schema is in 3NF iff for every functional dependency the determinant is a superkey or the dependent is prime; a relation schema is in BCNF iff every determinant is a superkey. A schema that is in 3NF but not in BCNF will have one or more determinants that are not superkeys. Find them and eliminate them.

*>
*

> 2) how correct is the following definition of transitive

*> dependencies
**>
**>
**> transitive dependencies
**>
**> assume that A,B, and C are the set of attributes of a relation(R).
**> further assume that the following
**> functional dependencies are satisfied simultaneously : A -> B , B -/-
**>> A, B -> C , and C -/-> A and A -> C
**> observe that C -> B is neither prohibited nor required. if all these
**> conditions are true, we will say that attribute C is transitively
**> dependent on attribute on A
**>
*

It is not correct: what if B = C or C is a subset of B? Received on Sat Aug 02 2008 - 10:10:39 CEST