File Management System

 File oriented approach of Organising data provides a set of facilitate users to organise, create, delete, update, and manipulate their files. All these programs together form a File management system (FMS). Features found commonly in file management system are described below:

File types

We categorize data files according to the way an application uses them. A file management system typically supports following types of files:

1. Transaction file:

A transaction file stores input data until the application uses it during next Processing cycle. For example, in a payroll application for generating monthly pay slips of employees, current month transaction file contains this month's data of each employee, such as details of hours worked, normal and overtime hours, and if peace work is involved, quantity of goods made.

2. Master file:

A master file contains all current data relevant to an application. For example, in payroll application mentioned above, master files contains payment details of each employee ( name, address, employee code, pay rate, income tax rate, etc.) And also current gross pay to date total and tax-paid-to-date total. When the user runs month cycle of payroll application, the application consolidate both master and current month's transaction files to generate this month's payslips, and updates master file to make it ready of following month's processing.

3. Output file:

Some applications use multiple programs for data processing. These applications often take output of one program and feed it as input to another program. The former program stores it output in a file known as output file, which the latter program uses later.

4. Report file:

A report file holds a copy of report, which a data processing application generates in computer accessible form. A user can print a report file to obtain hardcopy of the report whenever desired. It is advantageous to keep report files inserted of paper documents because files are easier to store and carry. 

5. Backup file:

A backup file is a copy of a file, which a user/system creates as a safety precaution against loss of data due to corruption or inadvertent deleting of original file. Regular creation of backup files is extremely important.

File utilities

File utilities are routines, which performs generic operations on data files. Normally, they are quite general in nature in the sense that they can deal with different data formats and different types of storage medium. Some commonly used file utilities are described below:

1. Sorting utility:

A file sorting utility arranges records of a file in some defined sequence. A user of sorting utility specifies value of certain fields (known as keys) of the files regards. The keys determine the sorting sequence of files records. The simplest case of sorting is ordering of records in a file on a single key. For example, the sequence of records of an employee file in figure (below) is ascending order of employee code, which is the key.

 A more complex sorting would be ordering of records in a file on two or more keys. For example, the sequence of records of employee file in figure ( below) is by ascending order of employee code within department code. Here employee code and department code are two keys. The sorting utility first lists all records for the lowest department code for each employee belonging to that department in ascending sequence of employee code, then all records for next department code, and so on. 

Out of this two keys in this sorting example, department code is called primary key, and employee code is called secondary key, because order of sorting is employee code within department code. 

A sorting utility enables users to specify their sequencing requirements for file by means of input parameters. Input parameters such as size and number of keys, and type of ordering ( ascending, descending) vary from one sorting utility to another. These parameters decide to extent and sophistication of sorting utilities. 

Sorting utility reads unsequenced records of an input file, and by means of various copying techniques, ultimately produces an output file containing records of the input file in desired sequence. 

2. Searching utility:

A file searching utility finds a particular record in a file. A user of searching utility specifies values of certain fields (known as keys) of the file's records. The searching utility matches the specified key values with their values in each record to search the desired record.

Efficiency of a search algorithm depends on file organisation. For example, to search in an sequential file, the search algorithm scans  the records of the  file sequentially, beginning with the first record. It compares the specified key field value with the key field value of each record  one by one. Search process terminates when the algorithm finds a record with matching key. On the other hand, direct or index sequential file organisations enable immediate access to a record with the help of either a hashing algorithm ( in case of direct file organisation) or an index file ( in case of index sequential file organisation). Users need to specify a file and key field value as input parameters to a search utility, which searches through the file and produces the desired record. Normally, searching a record form a direct or index sequential file requires much less time than searching  a record form a sequential file.

3. Merging utility:

A file merging utility combines records of two or more ordered (sorted ) files into a single ordered file. Merging utility requires the record of each input file be sorted in the same order, although their records layout need not be identical. A merging utility places regards from each of the input files in their currect relative order, producing an output file having all records in the same order as input files.

4. Copying utility:

A file copying utility produces a copy of a file either form the unit of a storage device to another similar unit ( such as from one tap reel to another ), or from storage medium to another ( such as from tap to hard disk, or from CD - ROM to hard disk).

Users often use file copying utility to take back up copies of files. For example, a user may copy a file form a hard disk to a tap for backup purpose. File copying utilities are also known as peripheral interchange programs (PIP) since users often use them to copy a file from one peripheral device to another.

5. Printing utility:

A file printing utility prints a file on a printer to produce hard copy of its contents. Printing utilities often provide the facility to print the file contents in different formats. They often provides some selection and editing facilities to enable printing of parts of files ( such as specified number of records and only certain fields of records). Some printing utilities provide special formats of printing files that contain program instructions rather than data.

6. Maintenance utility:

A file maintenance utility copies data from one or more files to a new file selectively, or updates a file's contents selectively. For example, a file maintenance utility may provide features to combine data from more than one file into a single file, delete a record from a file by specifying it's key value or record count, and select and copy specific fields of records from an existing file to a new file.