Dependency preservation, Database Management System

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."

 

Posted Date: 3/7/2013 2:23:40 AM | Location : United States







Related Discussions:- Dependency preservation, Assignment Help, Ask Question on Dependency preservation, Get Answer, Expert's Help, Dependency preservation Discussions

Write discussion on Dependency preservation
Your posts are moderated
Related Questions
Entities Let us first be aware of the question: What are entities? An entity is an object of concern used to show the things in the actual world, e.g., table, car, bo

What is Asterisk in SQL? Asterisk (*): In SQL, the columns for all the tables and views in the FROM clause will be displayed.

What is a guard condition? Explain it with a suitable example. The guard-condition is a Boolean expression written with respect to parameters of triggering event and attributes

Q.   With the help of a suitable diagram gives module wise explanation of system architecture of DBMS. Sol. A Database management is a collection of interrelated data and col

to develop elrctronic database from manual forms

What is a query tree?     Ans:  A query tree, as well known as operator graph, is a tree data structure that corresponds to a relational algebra expression. It denotes the inpu

Explain the disadvantages of file oriented approach? In the oriented approach Applications are designed in isolation. Design of application is optimized for one application. In

The indices are accumulated in the index files. The data is accumulated in the data files. Indices give fast access to data items. For example, a book database may be managed in th


State the Steps of Object Design Object design is a very iterative process in which various classes, relationships among objects are added when you move from one level to