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

DW, #ques Define a job scheduling strategy that will meet business requirem...

#ques Define a job scheduling strategy that will meet business requirement of reporting availability by 6am CST for the following cubes? Show the job scheduling dependencies in a p

Normalization, Normalize the given relation to 3NF, justifying each step

Normalize the given relation to 3NF, justifying each step

Estimate the transaction states, Suppose an instruction takes 1 nanosecond ...

Suppose an instruction takes 1 nanosecond to execute (on average), a page fault takes 20 microseconds of processor time, and it takes 300 microseconds of disk time to read or write

Binary relationships, One-to-one relationship: For every 1:1 relationshi...

One-to-one relationship: For every 1:1 relationship type R in the ER diagram including two entities E1 and E2 we take one of entities (say E1) preferably with total participatio

Explain about sql server 2000, What is the difference between SQL Server 2...

What is the difference between SQL Server 2000 complete and differential backups? A complete backup makes a copy of the whole database. A differential backup creates a copy of

Software failures-database recovery and security, Software failures :  In s...

Software failures :  In such cases, a software error abruptly stops the implementation of the current transaction (or all transactions), therefore leading to losing the state of pr

Create table employee and enter employee data in sql, Create table employee...

Create table employee and enter employee data in SQL? Consider the following relational schemas: EMPLOYEE (EMPLOYEE_NAME, STREET, CITY) WORKS (EMPLOYEE_NAME, COMPANYNAME, SAL

Can a domain, Can a domain, assigned to a data element be changed? Yes....

Can a domain, assigned to a data element be changed? Yes.  We can do so by just overwriting the entry in the field domain.

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