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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
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How does a query tree represent a relational algebra expression? Discuss any three rules for query optimisation, giving example as to when should each rule be applied. Ans
Physical Records These are the records that are stored in the secondary storage devices. For the database relation, physical records are the group of fields kept in adjacent me
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A student entity type has the following attributes,name..
Hi I have got an assignment for making an er diagram for market management software can any budy help me?
What is vertical fragmentation? Vertical fragmentation divides the relation by decomposing the scheme R of relation r.
Which is another name for weak entity? Child is another name of weak entity.
Project Description: Oracle Certified Professional with 20 years of practice, Oracle version 6.0.34, 7.3, 8.0, 8i, 9i, 10G, 11G, 12C. Crossplatform migration, Informix, MSSql
What are the technique to define a schema completely ? A schema is completely define by DDL and DML query language.
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