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 gathering information and producing erd, What is Gathering informat...

What is Gathering information and Producing ERD Gathering information: This could be a written document that explains the system in question with reasonable quantity of detai

Hashing techniques, folding method and mid square method using visual basic...

folding method and mid square method using visual basic

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

Give the forms of triggers, Give the forms of triggers? The triggering ...

Give the forms of triggers? The triggering event can be insert or delete. For updated the trigger can state columns. The referencing old row as clause The referencing

Hardware failure-database recovery and security, Hardware failure :  Hardwa...

Hardware failure :  Hardware failures are the failures when some disk or hardware chip fails. This may result in loss of data. One such trouble can be that a disk gets damaged and

Can your organization scan large format documents, Can your organization sc...

Can your organization scan large format documents? Yes, large format scanning used for such entities as city plans and blueprints is available. We selected scanners with the ab

Define outer union operation of the relational algebra, Define outer union ...

Define outer union operation of the relational algebra. Compute the outer union for the relations R and S given below. Outer Join - If there are any values in one tabl

Key constraint - relational constraints, This constraint shows that the key...

This constraint shows that the key attribute value in each tuple must be unique, i.e., no two tuples have the similar value for the key attribute. This is because the value of the

Define the canonical cover, Define the Canonical cover Ans: A canonical...

Define the Canonical cover Ans: A canonical cover F c for F is a set of dependencies like F logically implies all dependencies in F c , and F c logically entails all dependen

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