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

When is a transaction rolled back, When is a transaction rolled back? A...

When is a transaction rolled back? Any changes that the aborted transaction made to the database must be uncompleted. While the changes caused by an aborted transaction have be

What is rdbms terminology for a row, What is RDBMS terminology for a row? ...

What is RDBMS terminology for a row? A tuple is a RDBMS terminology for a row

What is index, What is Index? An index is a physical structure having p...

What is Index? An index is a physical structure having pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possibl

Draw an er diagram for organization of a student database, Draw an ER diagr...

Draw an ER diagram that shows the organization of a simple student database. The database captures the information about letter grades obtained by university students who enrolled

Illustrate the view of software architecture, Illustrate the view of softwa...

Illustrate the view of software architecture A model is a semantically closed abstraction of system composes of elements. It can be visualized using any of the following five v

Objectives-the structured query language, Objectives After reading this...

Objectives After reading this part, you should be able to: Modify, create, and delete database schema objects; Update database using SQL command; Retrieve data f

Hoework, Farmer Bob, Farmer Jane and Farmer Jose run a cow farming co-op. ...

Farmer Bob, Farmer Jane and Farmer Jose run a cow farming co-op. For every cow they keep the cow’s name, age (or date of birth), breed and numbered plastic ear tag. The each of t

Cost of reading a file , A file of employee have 10,000 blocks on a cylinde...

A file of employee have 10,000 blocks on a cylinder of a disk with characteristics r=8ms and btt=0.6ms I want to know the cost of read inthe file under following conditions for a q

What is the use of with clause in sql, What is the use of with clause in SQ...

What is the use of with clause in SQL? The with clause gives a way of defining a temporary view whose explanation is available only to the query in which the with clause occurs

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