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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
Determine the term- Active values An active value is that has dependent values. Every dependent value registers itself with active value that contains a set of dependent values
System level permissions : With the use of data dictionary you can view them. Let us take the table name as user_sys_privs (used in oracle). DESCRIBE USER_SYS_PRI
online eductional management system ke diagram
What are multiple inheritances? Multiple inheritances allow a class to inherit variables and methods from many super classes.
Question: (a) Use the following business rules to produce the E-R diagram. You should clearly show all the minimum and maximum cardinality constraint on each side of the relati
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Replication : It is definite as a copy of a relation. Every replica is stored at a dissimilar site. The alternative to replication is to store only single copy of a relation which
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