Primary and foreign key, Database Management System

Assignment Help:

Primary Key

The primary key is the candidate key that is selected by the database designer as the principal denotes of identifying entities within an entity set. The left candidate keys, if any, are called as alternate keys.

Foreign Keys

Let us first tell you the basic definition of foreign key.

Let R2 be a relation, then a foreign key in R2 is a subset of the set of attributes of R2, such that:

1.   There be a relation R1 (R1 and R2 not essentially distinct) with a candidate key, and

2.   For all time, every value of a foreign key in the present state or instance of R2 is identical to the value of Candidate Key in a few tuple in the present state of R1.


Related Discussions:- Primary and foreign key

Data manipulation language, Question 1 Discuss about second normal form an...

Question 1 Discuss about second normal form and third normal form Question 2 Write short note on                        1) Data Manipulation Language 2) Data Definition La

What is message switching, What is Message switching Message switching ...

What is Message switching Message switching transmits data units which can be arbitrarily long. Packet switching has a utmost packet size, if any message longer than that, it s

What is repository?, Problem 1 Why are the operational system keys not ...

Problem 1 Why are the operational system keys not recommended for forming data warehouse primary keys? Give any two examples 2 Explain the following performance tuning techn

Determine the object-oriented design process, An object-oriented design pro...

An object-oriented design process  1. Define the context and modes 2. Designs the system architecture 3. Identifies the principal system objects 4. Identifies concurrency in

Define blocks, Define blocks? The database system resides eternally on ...

Define blocks? The database system resides eternally on non-volatile storage, and is into fixed-length storage units known as blocks.

Backup - restore utilities, These are designed to reduce the effects of a d...

These are designed to reduce the effects of a database failure and make sure a database is restored to a consistent state if a failure does arise. Manual backup/restore utilities n

Discuss the different layers of ansi sparc architecture, Q.1 Briefly discus...

Q.1 Briefly discuss the different layers of ANSI SPARC architecture. Ans: The three layers of ANSI SPARC architecture are like this: 1. Internal view is at the lowest leve

Develop and evaluate partial systems, Part 1: Security Plan Consider th...

Part 1: Security Plan Consider the Case study and identify 3 security requirements. For each of these security requirements: • Discuss the necessity for the feature and how

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