File Organization in DBMS

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Friends, we have already discussed the Introduction and a few Important Topics of Data Base Management Systems (you can read them from here). Today we shall discuss about another important topic of DBMS, the file organization. A file organization is defined as arranging the records in a file when the file is stored on disk. A file or records can be accessed and modified in a variety of ways, and different ways of arranging the records enable different operations over the file to be carried out efficiently.

Examples :

1. To retrieve employee records in alphabetical order, sorting the file by name is a good file organization.
2. To retrieve all employees whose salaries are in a given range, sorting employees records by name is not a good file organization. 

A DBMS, supports several file organization techniques, and an important task of a DBA (Data Base Administrator) is to choose a good organization for each file, based on its expected patter of use. 

The three different file organizations are :

1. Heap File Organization : Files of randomly ordered records are called Heap files. Records are placed in the  file in the order in which they are inserted. New records are inserted at the end of the file. In simple words we can say that just throwing the files as they are (unordered) is called heap organization.
2. Sorted File Organization : In this organization the files are sorted on a sequential order.
3. Hashed file Organization : Files that are hashed on some fields are called hashed files. This provides fast access to records on certain search conditions. In a hash file, records are not stored sequentially in a file instead a hash function is used to calculate the address of the page in which the record is to be stored. In this organization, the records are randomly distributed in the file so we can also call it as Random or Direct files.

Hareesh Reddy. K

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