FILE ORGANIZATION TYPES OF FILE ORGANIZATION n n

FILE ORGANIZATION

TYPES OF FILE ORGANIZATION n n Serial Sequential Indexed Sequential Direct Access /Random Access

Serial File Organization n n 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 n n A collection of records Stored in key sequence Adding/deleting record requires making new file Used as master files

Sequential file

The Sequential File organization

The Sequential File organization n To enable a sequential form of records, new records are placed in a log file or transaction file. Then, a batch update is performed to merge the log file with the master file to produce a new file with the correct key sequence

Advantages n n 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 n n n 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 n 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 n A random file would have to be stored on a direct access backing storage medium e. g. magnetic disc, CD, DVD n Example : Any information retrieval system. Eg Train timetable system.

Advantages n n 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 n n n More complex than sequential Does not fully use memory locations More security and backup problems

Indexed sequential file n n 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 n Indexed sequential files are important for applications where data needs to be accessed. . . q q sequentially randomly using the index.

Indexed sequential file n An indexed sequential file can only be stored on a random access device e. g. magnetic disc, CD.

Advantages n n Provides flexibility for users who need both type of accesses with the same file Faster than sequential

Disadvantages n Extra storage space for the index is required

Files I/O in c n n fopen() function It requires two arguments: 1. File Name 2. option(r, w, a, etc)

Batch Processing n n n Batch processing is updating master files periodically to reflect all transactions that occurred during a given time period. The master file is updated at set times or whenever a manageable number of transactions are gathered. Transaction data can either be entered as a batch or as each transaction occurs.

Batch Processing Group source documents into batches. Master file

On-line Batch Processing Enter transactions into system as they occur. Master file

On-line, Real-Time Processing n In on-line, real-time processing, the computer captures data electronically, . . . – – n edits it for accuracy and completeness, and. . . immediately processes it. The computer also processes information requests from users.

On-line, Real-Time Processing Enter transactions into system as they occur. Master file

Advantages of Each Method n n n The main advantage of batch processing was efficiency in processing. On-line data entry is more accurate than periodic batch input because the system can refuse incomplete of erroneous entries. Real-time processing ensures that the information in master files is always current.