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Sunday, October 9, 2016

Relational Models-Tutorial

Logical view of Data

In the database, all the records are stored in the physical memory in the form of bits in the files. But the user will see all these in the form of rows and columns. This user view is called logical view of the data. User will not have any information about how it will be stored in the memory. He views the data in the form of tables. This is easy for anyone to understand.
For example, STUDENT records will be scattered in the memory in various data blocks in the form of bits. But when user fetches the data, he will view it in the form of table. Different subset of records can be created out of main table and named. This named subset of records in a database is known as views. This is also can be viewed as tables.
The tables in the database are related to one another by using the mapping / relation. This is achieved by using one of the parent table columns in the child table. The parent table column in the child table is known as foreign key column.

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