Boyce-codd normal form (bcnf), Database Management System

Boyce-Codd Normal Form (BCNF)

The relation NEWSTUDENT (Enrolmentno, Sno, Sname, Cname, Cno,) has every attributes participating in candidate keys as all the attributes are assumed to be unique. We thus had the following candidate keys.

(Enrolmentno, Cno)

(Enrolmentno, Cname)

(Sname, Cno)

(Sname, Cname)

As the relation has no non-key attributes, the relation is in 2NF and as well in 3NF. Though, the relation suffers from the anomalies (please check it yourself by making the relational instance of the NEWSTUDENT relation).

The complexity in this relation is being caused by dependence within the candidate keys.

Definition: A relation is in BCNF, if it is in 3NF and if each determinant is a candidate key.

  • A determinant is the left side of an FD
  • Most relations that are in 3NF are also in BCNF. A 3NF relation is not in

BCNF if all the following conditions apply.

(a)     The candidate keys in the relation are composite keys.

(b)     There is more than one overlapping candidate keys in the relation and a number of attributes in the keys are overlapping and some are not overlapping.

(c)      There is a FD from the non-overlapping attribute(s) of single candidate key to non-overlapping attribute(s) of other candidate key.

Let us recall the NEWSTUDENT relation:

NEWSTUDENT (Enrolmentno, Sname, Sno,  Cno, Cname) Set of FDs:

Enrolmentno     →           Sname              (1)

Sname  →                       Enrolmentno     (2)

Cno       →                      Cname              (3)

Cname  →                      Cno                   (4)

The relation even though in 3NF, but is not in BCNF and can be decomposed on any one of the FDs in (1) & (2); and any one of the FDs in (3) & (4) as:

STUD1 (Enrolmentno, Sname) COUR1 (Cno, Cname)

The third relation that will join the two relation will be:

ST_CO(Enrolmentno, Cno)

Since this is a slightly complex form, let us give one more example, for BCNF. Consider for example, the relation:

ENROL(Enrolmentno, Sname, Cno, Cname, Dateenrolled)

Let us suppose that the relation has the following candidate keys:

(Enrolmentno, Cno)

(Enrolmentno, Cname)

(Sname, Cno)

(Sname, Cname)

(We have supposed Cname and Sname are unique identifiers).

The relation has the following set of dependencies:

Enrolmentno     →    Sname

Sname             →     Enrolmentno

Cno                  →     Cname

Cname             →     Cno

Enrolmentno, Cno     →  Dateenrolled

The relation is in 3NF but not in BCNF as there are dependencies. The relation suffers from all anomalies. Please draw the relational instance and checks these troubles. The BCNF decomposition of the relation would be:

STUD1 (Enrolment no, Sname)

COU1 (Cno, Cname)

ENROL1 (Enrolmentno, Cno, Dateenrolled)

We now have a relation that only has information about students, another only about subjects and the third only about relationship enrolls.

Posted Date: 3/7/2013 2:08:57 AM | Location : United States







Related Discussions:- Boyce-codd normal form (bcnf), Assignment Help, Ask Question on Boyce-codd normal form (bcnf), Get Answer, Expert's Help, Boyce-codd normal form (bcnf) Discussions

Write discussion on Boyce-codd normal form (bcnf)
Your posts are moderated
Related Questions
What is the difference between link and reference? The fundamental difference between links and references is that links are symmetrical on the other hand references refer only

what is Mapping Constraints? with examples

A distributed database is defined as "a collection of multiple logically interrelated database which are physically distributed over a computer network" (a) Give any three advan

What is Candidate Key Super Key or Candidate Key: It is such an attribute of a table that can uniquely recognize a row in a table. Generally they have unique values and can n

using the invoice table shown below,write the relational schema,draw a dependencies,inclunding all partial and transitive dependencies.assume that the table does not contain repeat

What is SQL Profiler? SQL Profiler is a graphical tool that permits system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save dat

Define the Traditional System Analysis and Design Traditional System Analysis and Design (SAD) have three basic life cycle models. A typical software lifecycle consists of the

The Maximum no of key fields that can be used in a header is?? 50

I want a professional with strong IT background who provide me timely assignments Project Description: I want a professional who can do my assignments for my major i.e. Infor

i need help for assignment ..