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Relations create the database. They must satisfy various properties, like no duplicate tuples, no ordering of tuples, and atomic attributes, etc. Relations that satisfy these basic needs may still have some undesirable characteristics such as data redundancy, and anomalies.
What are these undesirable characteristics and how can we eliminate them from the database system? This part is an attempt to answer this question. Though, please note that most of these undesirable properties do not arise if the database modelling has been carried out very carefully using some method like the Entity-Relationship Model. It is still important to use the methods in this unit to check the database that has been acquired and ensure that no mistakes have been made in modeling.
The central thought in these discussions is the concept of Database integrity, the notion of functional dependency, which rely on understanding the semantics of the data and which deals with what information in a relation is dependent on what other information in the relation. Our prime objective in this section is to describe the concept of data integrity, functional dependence and then describes normal forms using functional dependencies and using other types of data dependencies.
OBJECTIVES
After reading this section you should be able to
Rules Of Data Normalisation Let us now summarise Normalisation with the help of various clean rules. The following are the necessary rules for the Normalisation process: 1.
What is catalog in DBMS? Catalog - A relational DBMS maintains information about every table and index in which it contains. A catalog is a collection of special tables that st
The technique of converting the state diagram to code a) Identify all major control paths. Start from initial state; choose a path across the diagram that corresponds to normal
The External or View Level The external or view level is the highest level of abstraction of database. It gives a window on the conceptual view, which permits the user to see
What are the basic objects of the data dictionary? Tables Domains Data elements Structures Foreign Keys
Briefly describe the different kinds of users of a DBMS. Ans: Different sorts of DBMS users are: (a) Software Engineers: These are the people accountable for developing ap
Type of database technology
Example: RELATIONAL SCHEMA for PERSON: PERSON (PERSON_ID: integer, NAME: string, AGE: integer, ADDRESS: String) RELATION INSTANCE In this instance, m = 3 and n = 4
Given the following set of functional dependencies {cf→ bg, g → d, cdg → f, b → de, d → c} defined on R(b,c,d,e,f,g) a. Is cf→ e implied by the FDs? b. Is dg a superkey?
Explain the function of Object model Object model describes the classes of objects in system, including their attributes and operations which they support. The analysis object
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