Candidate keys, Database Management System

Assignment Help:

Super keys of a relation can have extra attributes. Candidate keys are minimal super key, i.e. such a key have no extraneous attribute. An attribute is known as extraneous if even after removing it from the key, create the remaining attributes still has the properties of a key.

The following properties must be satisfied by the candidate keys:

  • A candidate key's value must exist. It cannot be null. (This is also known as entity integrity rule)
  • A candidate key has to be unique.
  • A candidate key is a smallest set of attributes.
  • The value of a candidate key has to be stable. Its value cannot change outside the control of the system.

A relation can have more than single candidate keys and one of them can be chosen as a primary key.

For instance, in the relation PERSON the two likely candidate keys are PERSON- ID and NAME (assuming unique names in the table). PERSON-ID may be taken as the primary key.


Related Discussions:- Candidate keys

Explain the attribute inheritance, Explain the Attribute inheritance An...

Explain the Attribute inheritance Ans: Throughout the rendering of the objects in a view, attribute sets of objects higher in the view hierarchy are inherited via objects below

Information infrasctructure., what factors might influence a company to out...

what factors might influence a company to outsource its IT infrascture.

Er model, explain the steps for reduction of er model into relational model...

explain the steps for reduction of er model into relational model?

Find the employee name, Example -Find the employee name, salary, department...

Example -Find the employee name, salary, department number and average salary of his/her department, for those employees whose salary is more than the average salary of that depart

List some instances of collection types, List some instances of collection ...

List some instances of collection types? a) sets b) arrays c) multisets

Define the boyce-codd normal form, Define the Boyce-Codd Normal Form with i...

Define the Boyce-Codd Normal Form with instance and also Compare BCNF and 3NF.  Ans: BCNF: For each functional dependency X->Y in a set F of functional dependencies over relati

Extended star schema, Why did SAP introduce the extended star schema? Expla...

Why did SAP introduce the extended star schema? Explain why it is reported to be better than the traditional schema model?

4, explain the level architectures of the database management system

explain the level architectures of the database management system

What are metrics for choosing the best algorithm, What are metrics for choo...

What are metrics for choosing the best algorithm? Matrices for choosing the best algorithms are as below: Computational complexity Ease of understand ability and im

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd