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

What is the main advantage of the object model, What is the main advantage ...

What is the main advantage of the object model? What are its different components? The object model focuses on the logical data structures. Each object model comprises of many

advantages of database over file system, Q.   Why would you choose a datab...

Q.   Why would you choose a database system instead of simply storing data in operating system file? Define  at a base concept in details. Sol. Advantages of Database over Fil

How is concurrency identified, How is concurrency identified? Concurren...

How is concurrency identified? Concurrency in objects can be identified by the way they alter their state. Current objects can change their state independently. Aggregation imp

Draw an e-r diagram and convert it to a relational schema, In an organisati...

In an organisation various projects are undertaken. Each projects can employ one or more employees. Every employee can work on one or more projects. Each project is undertaken on

How can you map null values to other values while display, How can you map ...

How can you map NULL values to other values while display? IF( ) , IFNULL( ) keywords are used to do so. They are 'LIMIT' is used for the following kinds of problems: 1) Ans

Multi-list file organisation, Multi-list file Organisation Multi-list f...

Multi-list file Organisation Multi-list file organisation is a multi-index linked file organisation. A linked file organisation is a logical organisation where physical orderin

Reflects organisational structure, Reflects organisational structure: Many ...

Reflects organisational structure: Many organizations are distributed over various locations. If an organisation has many offices in dissimilar cities, databases used in such an ap

Enforce referential integrity, Use Access 2007 to create a database calle...

Use Access 2007 to create a database called UniLib.mdb. - this file should be created on your personal drive at the university (or C: if you're using Access 2007 at home) and t

Explain data independence, Explain data independence ? Data independenc...

Explain data independence ? Data independence is the capacity to modify the schema at one stage of a database system without having to change the schema at the further level.

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