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

Construct a generalization-specialization hierarchy, Construct a generaliza...

Construct a generalization-specialization hierarchy for a motor-vehicle sales company. The company sells motorcycles that comprise an engine number and cost; cars that have a chass

Query to list the employee name have 10000 salary, Consider employee table ...

Consider employee table of (i) and list names of department(s) for which average salary for department is more than 10,000. (SELECT d_name FROM dept WHERE d_code IN (SELECT d_c

Define query optimization, Define query optimization. Query optimizatio...

Define query optimization. Query optimization refers to the process of search the lowest -cost method of evaluating a given query.

Fragmentation, let us consider a table having 2200 records and the fixed si...

let us consider a table having 2200 records and the fixed size of the table to be considered as 25.then how many numbers of table is requredto perform horizontal fragmentation

Express types of information available in mysql, Express types of informati...

Express types of information available in MySQL? Information as regards the result of queries:  This includes number of records affected by any SELECT or UPDATE or DELETE st

Design a large scale system, Question: (a) Why is it important to know...

Question: (a) Why is it important to know the architecture rather than to start requirement capture when designing a large scale system? (b) Who are the different people in

List any two disadvantages of a database system, List any two disadvantages...

List any two disadvantages of a database system ? The disadvantages of database system are: • Database systems are difficult, complex, and time-consuming to design. • Substanti

What are the parts of sql language, What are the parts of SQL language? ...

What are the parts of SQL language? The SQL language has various parts: data - definitition language  Data manipulation language  View definition  Transaction contr

What are composite attributes, What are composite attributes? Composite...

What are composite attributes? Composite attributes can be separated in to sub parts.

Benefits of views-data control, Benefits: It limits data access. ...

Benefits: It limits data access. It makes difficult queries look easy. It permits data independence. It presents dissimilar views of the similar data.

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