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File organization

This document discusses different types of file organization, including serial, sequential, direct access/random access, and indexed sequential. Serial files store records in the order received with no particular sequence. Sequential files store records in key sequence and are used as master files. Direct access files allow any record to be accessed directly by calculating its address from a key field. Indexed sequential files combine the sequential ordering of records with a full index to allow both sequential and random access by key.

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A PRESENTATION ON FILE ORGANIZATION By Ganesh V.Pawar
FILE ORGANIZATION
TYPES OF FILE ORGANIZATION  Serial  Sequential  Indexed Sequential  Direct Access /Random Access
Serial File Organization  A collection of records  No particular sequence  Cannot be used as master  Used as temporary transaction file  Records stored in the order received
Sequential File Organization  A collection of records  Stored in key sequence  Adding/deleting record requires making new file  Used as master files
Sequential file
Advantages  Simple file design  Very efficient when most of the records must be processed e.g. Payroll  Very efficient if the data has a natural order  Can be stored on inexpensive devices like magnetic tape.
Disadvantages  Entire file must be processed even if a single record is to be searched.  Transactions have to be sorted before processing  Overall processing is slow
Direct (Random) File Organization  Records are read directly from or written on to the file.  The records are stored at known address.  Address is calculated by applying a mathematical function to the key field.
Direct (Random) File Organization  A random file would have to be stored on a direct access backing storage medium e.g. magnetic disc, CD, DVD  Example : Any information retrieval system. Eg Train timetable system.
Advantages  Any record can be directly accessed.  Speed of record processing is very fast.  Up-to-date file because of online updating.  Concurrent processing is possible.
Disadvantages  More complex than sequential  Does not fully use memory locations  More security and backup problems
Indexed sequential file  Each record of a file has a key field which uniquely identifies that record.  An index consists of keys and addresses.  An indexed sequential file is a sequential file (i.e. sorted into order of a key field) which has an index.  A full index to a file is one in which there is an entry for every record.
Indexed sequential file
Indexed sequential file  Indexed sequential files are important for applications where data needs to be accessed..... – sequentially – randomly using the index.
Indexed sequential file  An indexed sequential file can only be stored on a random access device e.g. magnetic disc, CD.
Advantages  Provides flexibility for users who need both type of accesses with the same file  Faster than sequential
Disadvantages  Extra storage space for the index is required