Entity integrity, Database Management System

Assignment Help:

Before defines the second type of integrity constraint, viz., Entity Integrity, we should be well-known with the concept of NULL.

Mostly, NULL is intended as a basis for dealing with the trouble of missing information. This type of situation is frequently encountered in the actual world. For instance, historical records sometimes have entries such as "Date of birth unknown", or police records may contain the entry "Present whereabouts unknown." Therefore it is necessary to have some way of dealing with such concepts in database systems.

Therefore Codd proposed an approach to this issue that creates use of special markers known as NULL to show such missing information.

A given attribute in the relation may or may not be allowed to include NULL. However, can the Primary key or any of its components (in case of the primary key is a composite key) contain a NULL? To answer this Query an Entity Integrity Rule states: No component of the primary key of a relation is permitted to accept NULL. In different words, the definition of each attribute involved in the primary key of any basic relation have to explicitly or implicitly contain the specifications of NULL NOT ALLOWED.


Related Discussions:- Entity integrity

Dataset, The dataset " CFOLYMPICS.XLS " contains the observations used in t...

The dataset " CFOLYMPICS.XLS " contains the observations used in the above article.  The definitions of the variables are also included in this spreadsheet.  However, for the purpo

Data modelling, Law Associates is a large legal practice based in Sydney.  ...

Law Associates is a large legal practice based in Sydney.  You have been asked to design a data model for the practice based upon the following specification: The practice emplo

Explain about foreign key, What is Foreign Key Foreign Key: Sometimes...

What is Foreign Key Foreign Key: Sometimes we may have to work with an attribute that does not have a primary key of its own. To recognize its rows, we have to use the primar

What is business intelligence, Question A What is operational intelligence...

Question A What is operational intelligence? Question B What is Business Intelligence? Explain the components of BI architecture Question C Differentiate between databas

Explain briefly concurrent task by taking an example, Explain briefly concu...

Explain briefly concurrent task by taking an example. Concurrent Task- The concurrent occurrence of more than one event is called concurrent task. Operating systems can handl

Command line interfaces, Command Line Interfaces: These are interactive int...

Command Line Interfaces: These are interactive interfaces, character-based that let you use the complete power and functionality of the DBMS query language directly. They permit yo

OLD HOME POLICIES, Write an sql statement to find what is the percentage of...

Write an sql statement to find what is the percentage of home policies which are from the state of Arizona out of all Home policies by Policy Value.

Cataloguing, differences between a classified catalog and a dictionary cata...

differences between a classified catalog and a dictionary catalog

Explain the form of the create view command, We define a view in SQL throug...

We define a view in SQL through using the create view command. To describe a view, we must provide the view a name and must state the query in which computers the view. The form of

What is sql server agent, What is SQL Server Agent? SQL Server agent pl...

What is SQL Server Agent? SQL Server agent plays a significant role in the day-to-day tasks of a database administrator (DBA). It is often overlooked as one of the major tools

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