Filing Systems
Typically a record corresponds to an entity and a field to an attribute.
The database on secondary storage is organised into one or more files, where each files consists of
one or more records and each record consists of one or more fields.
We can expect that a tuple will map onto a record in the Operating System file that holds the Staff
Relation in the earlier example. Each field in a record would hold an attribute.
When a users requests a tuple the DBMS maps this logical record onto a physical record and
retrieves the physical record into the DBMS buffers using the OS file access routines.
The Physical record is the actual unit of transfer between the disk and RAM and is usually more
than one logical record. Physical records are also sometimes referred to as blocks or Pages.
The order in which the records are stored and accessed in the file depends upon the file
organization; this is the physical arrangement of data in a file into records and pages on disk.
The common File Organisations are :
• Sequential File
• Random or Direct File
• Indexed File
Read about these file organization techniques and make notes on how they work and explain the
differences between them.
Questions
Which type of file organization would use ISAM.
Which type of file organization would use Hashing?