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

What is document scanning and imaging, What is document scanning and imagin...

What is document scanning and imaging? Document scanning and imaging, or digital archiving, is the method of scanning a document into a digital image to archive and retrieve a

Extended e-r features, Although, the essential features of E-R diagrams are...

Although, the essential features of E-R diagrams are enough to design many database situations. Though, with more difficult relations and advanced database applications, it is need

What is theta join explain, What is theta join explain? Theta  Join  -...

What is theta join explain? Theta  Join  - The  theta  join  operation  is  an  extension  to  the  natural-join operation which permits us to merge selection and a Cartesian

Explain instance and schemas, Explain Instance and schemas? Instances ...

Explain Instance and schemas? Instances and schemas: Databases changes over time as the information is deleted and inserted. The collection of information stored in database

Entity - relation modeling and transformation, Represent the following scen...

Represent the following scenarios with E-R diagrams drawn using the ER Assistant software. The diagrams should indicate cardinality and optionality of relationships. Transform each

Define thomas write rule, Define Thomas write rule Thomas' write rule: ...

Define Thomas write rule Thomas' write rule: The Thomas' write rule is a modification of timestamp-ordering protocol for concurrency control. Assume that transaction T i issue

Which language used in application programs for request data, Which languag...

Which language used in application programs to request data from the DBMS is referred? Language which is used in application program is DML to request data from the DBMS is ref

What is structured query langauge, What is Structured Query Langauge (SQL)?...

What is Structured Query Langauge (SQL)? SQL is a powerful set-oriented language which was formed by IBM research for the databases that adhere to the relational model. It havi

What is multivalued attribute, What is Multivalued Attribute? Multival...

What is Multivalued Attribute? Multivalued Attribute - Multivalued attribute might have more than one value for an entity. For instance, PreviousDegrees of a STUDENT.

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