METHODS OF FILE ORGANIZATION AND ACCESS

File organization and access relates to the use of records, fields and files, it deals with how data
is stored on files and how files are stored on a storage medium.

Files have three important characteristics

1. Whether the file is permanent or temporary

2. The way the records are organised – sequential, or serial

3. Method of access or location – sequential or direct access

Types of Files

Master File: This is a permanent file which is kept up to date and stores the main information,
summary data and key fields in the data. The master file contains two types of data:

· Permanent data such as personal files, payroll data, employee status (contract, permanent or
temporary) and job title.

· Less permanent data such as taxes deducted, hours worked, bonuses received.

Transaction File: This is a temporary file which is used to update the master file after a certain
time; usually at the end of the day or at the end of the week. Transaction files perform three
important tasks:

· Add a new record to the master file

· Update or change the contents of a record or field.

· Remove records from the master file such as employee dismissal.

Serial file organisation is the simplest type of file organisation. The records are arranged one
after another in the order in which they were added. That is, they have not been sorted into any
particular order. Examples of serial files (also called unordered files). A serial file is mainly used
for backup purposes and is stored on tape or disk.

Examples of serial files

1. Unsorted invoices for customers

2. Collection of student marks

3. Shopping list

Sequential File organisation

A sequential file is one in which the records are stored in sorted order or sequential order on
one or more key fields.

Examples of sequential files

1. Invoices for customers sorted on customer number

2. Class registers sorted on last name

Indexed Sequential File organisation

An indexed file is used to speed up the key search in a file. You can think of it as a one –column
table organised in ascending order and stored on disk. The primary key in the table is used as an
index to the record. Index sequential file can be considered to be a sequential file that uses an
index.

Random File Organisation

Like index- sequential files, random files can only be used on direct access media, such as disks.
Random file organisation is the most efficient way of storing extremely large files, such as
National databases. Random files use a very clever method of providing direct access to records.
Each record will have its own specific position or address on the disk. The records are not sorted
in any way. The position allocated to each record will be calculated by using a special formula.
Advantages of Sequential File organisation

1. Accessing of records is fast, if the index table is properly organized.

2. Both sequential and random access is possible

Disadvantages of Sequential File organisation

1. More storage space is needed due to the presence of index.

2. Less efficient in the use of storage space as compared to other file organizations.

File Access
This refers to the methods and techniques employed to read and write data from devices.

Serial Access

A method of access to data in which blocks are read from the storage medium in the physical
order in which they occur, until the required item is reached.

Sequential access means that records are accessed one by one in the order they are stored
until the right one is located. Serial access is similar, as you can access the records in the
same manner in which they were stored.

Advantages

1. Simple to understand

2. Easier to organize and maintain

Disadvantages

1. Searching is time consuming

2. Transactions must be sorted in a particular sequence before processing

Random access or direct access allows you to access the record you want without having to
go through any others, unlike sequential access.

APPLICATION AREAS

■ Archiving – This is the process of moving files that are no longer actively used to a
separate storage device for long-term retention. Archived files are still important to the
organisation and may be needed for future reference or must be retained for regulatory
compliance. Files that are archived may be accessed in a serial manner or directly,
depending on the file organisation method used.

■ Payroll file – The employee payroll file is the source for everything that has to do with an
employee’s pay cheque. It would include information about the employee’s gross salary,
deductions, net pay, etc. The main reason to create a payroll file, which is likely to be stored
in a sequential manner, is to limit access to the rest of the confidential information that is
located in the personnel file.

■ Real-time systems – This is a software system where the correct functioning of the system
depends on the results produced by the system and the time at which these results are
produced. This system is time-critical and thus, real-time systems must respond within a
specified period of time. Typical examples of real-time systems include air traffic-control
systems, networked multimedia systems, command-control systems, etc. Thus, direct file
organisation would be best suited for this application.