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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
How nulls are treated in comparison operator? Along with comparison (relational) operators, the null values are ignored as we cannot derive the relation along with the given op
Decompose the table with the following description and functional dependencies into a set of equivalent tables normalized to 3NF or BCNF. This database stores records from a (ve
What is known as clustering file organization? In the clustering file organization, records of several dissimilar relations are stored in the similar file.
Domain Constraints Domain constraints are primarily formed for defining the logically correct values for an attribute of a relation. The relation allows attributes of a relatio
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Why were functional methods fashionable in early days? These are inspired directly by computer architecture and thus popular among computer scientist in early days. The divisio
Cyber Transit Ltd keeps up-to-date information on the processing and current position of each dispatched item. Dispatched items are the main concern of the Cyber Transit product tr
What is D command work in the respect of QBE? D: It is the command inside QBE to delete tuple(s) from the relation.
What is the full form of ODBC ? ODBC stands for Open Database Connectivity.
write on the various type of relationalkey
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