Dependency preservation, Database Management System

Assignment Help:

Dependency Preservation

It is obvious that the decomposition must be lossless so that we do not lose any information from the relation that is decomposed. Dependency preservation is another main requirement since a dependency is a constraint on the database. If each attributes appearing on the left and the right side of a dependency appear in the similar relation, then a dependency is considered to be preserved. Therefore, dependency preservation can be checked simply. Dependency preservation is important, because as stated previously, dependency is a constraint on a relation. Therefore, if a constraint is split over more than one relation (dependency is not preserved), the constraint would be complex to meet. We will not talk about this in more detail in this unit.  You may refer to the more readings for more details. Though, let us state one basic point:

"A decomposition into 3NF is lossless and dependency preserving whereas a decomposition into BCNF is lossless but may or may not be dependency preserving."

 


Related Discussions:- Dependency preservation

Functional dependency in entities, FDs in Entities : Student entity : ...

FDs in Entities : Student entity :                                                Enrolment number →  Student name, Address Course Entity :

What are the advantages of using a dbms, What are the advantages of using a...

What are the advantages of using a DBMS? The benefits of using a DBMS are a) Controlling redundancy b) Restricting unauthorized access c) Giving multiple user interfac

Describe specialsation and generalization, Describe Specialsation and gener...

Describe Specialsation and generalization? Specialisation /generalization: This is a top down and bottom up approach to the design of database. It displays the IS_A relation

Search the salary of employees who are not ‘analyst’ , Example- Search the ...

Example- Search the salary of employees who are not 'ANALYST' but get a salary below than or equal to any people employed as 'ANALYST'. SELECT EMPNO, ENAME, JOB, SAL FROMEMP

Scope of traffic data management, A TDMS project plan is not a typical Info...

A TDMS project plan is not a typical Information Technology project plan; therefore, a traffic data project has several unique characteristics: Traffic data management system

What is a state chart diagram, What is a state chart diagram? State dia...

What is a state chart diagram? State diagrams (State Chart Diagram) explain all possible states that a particular object can get into, and how object's state changes as result

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