Deletion anomalies-data redundancy, Database Management System

Deletion Anomalies: Loss of important Information: In some cases, useful information may be lost when a tuple is deleted. For instance, if we delete the tuple corresponding to student 050111341 enrolled for MCS-014, we will misplace relevant information about the student by enrolment number, address and name of this student.  Likewise deletion of tuple having Sname "Rahul" and Cno 'MCS-012" will result in failure of information that MCS-012 is named computer organisation having an instructor "Anurag Sharma", whose office number is 105. This is known as deletion anomaly.

The anomalies arise primarily as the relation STUDENT has information about students as well as subjects. One solution to the troubles is to decompose the relation into two or more smaller relations. But what should be the basis of this decomposition? To solution the questions let us attempt to formulate how data is related in the relation with the help of the following Figure:

                              2336_Deletion Anomalies.png

 

                                                       Figure :  The dependencies of relation

Please note that the arrows in Figure are defines data inter-relationship. For instance, enrolment no column is unique for a student so if we identify the enrolment no of a student we can uniquely describe his/her name and address. Likewise, the course code (Cno) uniquely defines course name (Cname) and Instructor (we are assuming that a course is taught by only single instructor). Please also note one vital interrelationship in Figure that is, the Office (address) of an instructor is relying on Instructor (name), assuming unique instructor names. The root cause of the being there of anomalies in a relation is determination of data by the components of the non-key and key attributes.

Normalisation includes decomposition of a relation into minor relations based on the concept of functional dependence to come over undesirable anomalies.

Normalisation few times can affect performance. As it results in decomposition of tables, few queries desire to join these tables to create the data once again. But such performance overheads are smallest as Normalisation results in minimisation of data redundancy and may result in minor relation sizes. Also DBMSs executes optimised algorithms for joining of relations and many indexing schemes that decrease the load on joining of relations. In any case the benefits of normalization normally overweigh the performance constraints. Normalisation does lead to more well-organized updates since an update that might have needs various tuples to be updated, while normalised relations, in general, need the information updating at only one place.

A relation that requires to be normalised may have a very large number of attributes. In such relations, it is almost impossible for someone to conceptualise all the information and recommend a suitable decomposition to overcome the troubles. Such relations require an algorithmic approach of searching if there are troubles in a proposed database design and how to remove them if they exist. The discussions of these algorithms are beyond the scope of this part, except, we will initial introduce you to the basic concept that supports the process of Normalisation of big databases. So let us first describes the concept of functional dependence in the subsequent part and follow it up with the thoughts of normalisation.

Posted Date: 3/7/2013 1:44:54 AM | Location : United States







Related Discussions:- Deletion anomalies-data redundancy, Assignment Help, Ask Question on Deletion anomalies-data redundancy, Get Answer, Expert's Help, Deletion anomalies-data redundancy Discussions

Write discussion on Deletion anomalies-data redundancy
Your posts are moderated
Related Questions
Q.  What is relational algebra and calculus? Explain the relational algebra operators :- Selection and predicate, set operation, joins and division. Sol. Relational Algebra

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 preservati

Describe multi key files

An ideal data dictionary should have everything a DBA wants to know about the database. 1 Conceptual, External, and internal database descriptions. 2.    Descriptions of attr

What is known as heap file organization? In the heap file organization, any record can be placed anywhere in the file where there is space for the record. There is no ordering

A file manipulation command that extracts some of the records from a file is called ? A file manipulation command that extracts some of the records from a file is called SELECT

Farmer Bob, Farmer Jane and Farmer Jose run a cow farming co-op. For every cow they keep the cow’s name, age (or date of birth), breed and numbered plastic ear tag. The each of t

Define According to the levels of abstraction, the schema at the intermediate level is called  Ans: As per to the levels of abstraction, the schema at the intermediate level is

What type of view of total database content? Data base content Conceptual view of total database contain.

Define the Boyce-Codd Normal Form with instance and also Compare BCNF and 3NF.  Ans: BCNF: For each functional dependency X->Y in a set F of functional dependencies over relati