File Organisation In Dbms

Introduction

Databases are used to store information. Usually, the principal operations we have to perform on database are those relating to:

• Retrieving data
• Creation of data
• Modifying
• Removing some information which we are sure is no longer useful or valid.

We have seen that in terms of the logical operations to be done on the data, relational tables give a good mechanism for the entire over tasks. Thus the storage of a database in a computer memory (on the hard disk, of course), is mainly concerned with the following issues:

• They require storing a set of tables, where every table can be stored as an independent file.
• The attributes in a table are closely related and, thus, often accessed together. Thus it makes sense to store the dissimilar attribute values in every record contiguously. In fact, is it essential that the attributes must be stored in the similar series, for each record of a table?
• It seems logical to store all the records of a table contiguously. Though, since there is no prescribed order in which records must be stored in a table, we may choose the series in which we store the dissimilar records of a table.

We shall see that the point (iii) between these observations is quite needful. Databases are used to store information in the form of files of records and are typically stored on magnetic disks. This section focuses on the file Organisation in DBMS, the access methods available and the system parameters related with them. File Organisation is the way the files are in order on the disk and access method is how the data can be retrieved based on the file Organisation.