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

Differance between join and outer join, Differentiate between join and oute...

Differentiate between join and outer join? Outer joins return all rows from at least one of the tables or views mentioned within the FROM clause, as long as those rows get toge

Describe application programming interface, Describe Application programmin...

Describe Application programming interface? Application Programming Interface - Commercial SQL implementations take one of the two primary techniques for involving SQL in a p

Define query processing, Define Query Processing Query processing is th...

Define Query Processing Query processing is the process of selecting the best plan or strategy to be employed in responding to a database request. The plan is then executed to

Processing arrays, 1. A company wants a report containing a breakdown of pa...

1. A company wants a report containing a breakdown of payroll by department. Input, which should be stored in 3 parallel arrays, includes each employee's department number, hourly

Storage of database on hard disks, Storage Of Database On Hard Disks At...

Storage Of Database On Hard Disks At this point, it is worthwhile to note the difference among the terms file Organisation and the access method. A file organisation shows to t

Basic set operation, These are the binary operations; i.e., each is applied...

These are the binary operations; i.e., each is applied to two relations or sets. These two relations can be union compatible excluding in case of Cartesian product. Two relations R

Explain the term- data flows, Explain the term- Data Flows Data Flows:...

Explain the term- Data Flows Data Flows: A data flow connects output of an object or process to input of another process or object. It represents an in-between data value wit

What are the three types of data sources, What are the three types of data ...

What are the three types of data sources used with ODBC? An ODBC file data source is a file that can be shared between database users. An ODBC system data source is one that is

Datamodels, explain thee diffrent types of data models

explain thee diffrent types of data models

Identify the candidate keys, Consider the following six relation schemes an...

Consider the following six relation schemes and their corresponding sets of functional dependencies. In each case identify a. All the candidate keys b. The highest normal for

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