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
crete a data base relationship model Entity: Students; Professors; Dormitories buildings; Attributes of students: Name; Address; Dorm;

It is not possible to make an ABAP/4 program, which having only Subroutines. False. We can make ABAP/4 program, which having only Subroutines.

Advantages of Observation  Methods: Bailey has pointed  out four  advantages of observation: 1. Superior in Data  Collection  on Non Verbal Behavior: When  a person  a opi

The ABC Bank authority now wants to create a database for their customers. So you are requested to modify your program of Assignment A3 as follows. The main program first displa

Question: One of the tasks a database management system must perform is to ensure that the data is still intact in the face of software and hardware failure. This task is known

Why is database design important?

A use case diagram giving a pictorial overview of user requirements and brief use case descriptions. As the case study contains only an outline of a business scenario, you will als

What is OMR? OMR (Optical Mark Recognition) is the translation of marks - or the absence of marks - but not the shape of the mark on forms that have small circles ("also called

(a) What is a Sub-Query? (b) What is the difference between a scalar sub-query and a tabular sub-query? (c) Write an equivalent SQL statement to get the Name of Product wh

Differentiate between a unique key and a primary key. - By default, clustered index on column are created by primary key while nonclustered index are created by unique key.