Keys - relational database integrity, Database Management System

Candidate Key:  In a relation R, a candidate key for R is a subset of the set of attributes of R, which have the differnt two properties:

(1)        Uniqueness:                No two distinct tuples in R have the similar value for the candidate key

(2)        Irreducible:                 No correct subset of the candidate key has the uniqueness property that is the candidate key.

Each relation must have at least one candidate key which cannot be reduced more. Duplicate tuples are not permitted in relations. Any candidate key can also be a composite key. For instance, (student-id + course-id) together can create the candidate key of a relation known as marks (student-id, course-id, marks).

Let us review the properties of a candidate key.

Properties of a candidate key

  • A candidate key has to be unique and irreducible
  • A candidate might be involving one or more than one attributes. A candidate key that contains more than one attribute is said to be composite.

But why are we interested in candidate keys?

Candidate keys are essential because they give the basic tuple-level identification mechanism in a relational system.

For instance, if the enrolment number is the candidate key of a STUDENT relation, then the solution of the query: "Find student details from the STUDENT relation having enrolment number A0123" will output at most one tuple.

Posted Date: 3/6/2013 6:30:24 AM | Location : United States







Related Discussions:- Keys - relational database integrity, Assignment Help, Ask Question on Keys - relational database integrity, Get Answer, Expert's Help, Keys - relational database integrity Discussions

Write discussion on Keys - relational database integrity
Your posts are moderated
Related Questions

what would go in order patient#, patient name, patien address, surgeon#, surgeon name, surgery date, surgery type, drug admin


FitAll Ltd is a company that manufactures clothes. Its processes are manual and there are stand-alone Information Systems that aid to manage them. The Information Systems were purc

Process of normalization is the integral part of designing a database. Justify this statement with suitable database design

The technique of converting the state diagram to code a) Identify all major control paths. Start from initial state; choose a path across the diagram that corresponds to normal

What is NULL? Give an example to described testing for NULL in SQL? The NULL SQL keyword is used to represent either a missing value or a value which is not applicable in a re

Redo Logs: Any database must have minimum two redo logs. These are the rules for the database; the redo logs record all modifies to the system objects or user objects. If any type

Explain the disadvantages of file oriented approach? In the oriented approach Applications are designed in isolation. Design of application is optimized for one application. In

Problem 1. Write an assembly program to find the smallest among two numbers Writing an assembly program to find the smallest among two numbers 2. Explain the intern