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

What is outer join, What is Outer join?  They can be employed while we ...

What is Outer join?  They can be employed while we want to keep all the tuples in R, or all those in S or all those in both relations in the result of the JOIN in spite of of w

Define database management system, Normal 0 false false fal...

Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

Entity identifier key attributes, An entity type usually has an attribute w...

An entity type usually has an attribute whose values are distinct for every individual entity in the collection. Such an attribute is known as a key attribute and its values can be

Database for Managers, I have to create a database about anything of my cho...

I have to create a database about anything of my choice. It has to contain 4 queries, and 4 forms. It can be anything as simple as a shoe inventory with numbers - is this a service

NORRMALIZATION, Home based assignment Consider an ORDER table with the foll...

Home based assignment Consider an ORDER table with the following attributes: • Order Number (ONo),Customer Number (CNo),Customer Name (CNa),Item Number (INo),Unit Price (UP), Quant

What are the uses of the information in the data dictionary, What are the u...

What are the uses of the information in the Data dictionary? The following information is directly taken from the Data dictionary: Information on fields displayed with

Using column aliases-data manipulation language, Using Column aliases E...

Using Column aliases Example: To print column names as NAME and ANNUAL SALARY SELECT ENAME "NAME", SAL*12 "ANNUAL SALARY" FROM EMP;

Describe the concept of aggregation, Aggregation Aggregation is strong...

Aggregation Aggregation is stronger form of association. It represents the "has-a" or "part-of" relationship. An aggregation association depicts a complex object which is comp

Query optimization, what is meant semantic query optimization? how does it ...

what is meant semantic query optimization? how does it differ from other query optimization techniques?

What is normalization, What is normalization? It is a method of analysi...

What is normalization? It is a method of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to attain the properties (1).Minim

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