Concept of Computer Files

Definition of Computer File

1. A computer file is defined as the smallest meaningful unit of data representation within a computer.
2. A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and usually on some kind of durable storage.

File Contents

On the atomic level, all the information in a file is binary, or just a series of ones and zeros. A computer file may contain;
i. Document: A document includes any file created by a user.
ii. Program: Program files contain instructions for the computer’s microprocessor.
iii. Data: Data files include all other files that aren’t programs or documents.

File Functions

Files are used to do one or more of the following functions:
a. They provide machine-executable code
b. They store application programs or operating system configuration
c. They store data used by the users such as Microsoft Word files.

Computer File Terms

1. Record: A record is a collection of related fields.
2. Field: Field is a single piece of information about an object. A is also defined as a space that holds specific parts of data from a set or a record. Examples of fields are NAME, ADDRESS, QUANTITY, AGE, etc.
3. Data element: A data element is the logical definition of a field
4. Data item: Data item is the actual data stored in the field

Types of Data Items

Each data element consists of only a single item. These items will have one of the three basic types: numeric, alphabetic and alpha-numeric.
Numeric data: Data consisting of digits and not letters of the alphabet or special characters.
Alphabetic data: Data consisting of letters and not digits or special characters.
Alpha-Numeric data: Data consisting of digits, alphabets as well as special characters.

File Organization

The term "file organization" refers to how data are stored in a file and, consequently, the method by which it can be accessed.

File organization Terms

a. Block: A block is the physical unit of transfer between the backing store and the main memory.
b. Bucket: A bucket is the logical unit of transfer between the backing store and the main memory.
c. Hit: A hit is the number of times a program or item of data has been accessed.

File organization Structure

Types of File Organization

There are mainly four types of file organization:
1. Serial file organization
2. Sequential file organization
3. Index file organization
4. Random file organization
Explanation
Serial file organization
Serial files are stored in chronological order, that is, as each record is received it is stored in the next available storage position. In general, it is only used on a serial medium such as magnetic tape.
Sequential file organization
Sequential files are files whose records are sorted and stored in ascending or descending on a particular key field.
Index file organization
Indexed Sequential file organization is logically the same as a sequential organization, but an index is built indicating the block containing the record with a given value for the Key field. An index is an alphabetical list of names, subjects, etc., with references to the places where they occur,
Random file organization
A randomly organized file contains records arranged physically without regard to the sequence of the primary key. Records are loaded to disk by establishing a direct relationship between the Key of the record and its address on the file, normally by use of a formula (or algorithm) that converts the primary Key to a physical disk address. This relationship is also used for retrieval.

Methods for Accessing Files

Files can be accessed:
a. Serially
b. Sequentially and
c. Randomly

File Classification

Files are classified as follows;
a. Transaction Files: transaction files contain details of all activities that have occurred in the last period. Examples of transaction files are the price of the products, customers' orders for the products, inserting new data into the database etc.
Features of transaction file
1. The data stored in these files are temporary by nature
2. Any data to be modified is done in this file

b. Master Files: Master files are permanent files kept up-to-date by applying the transactions that have occurred during the operation of the business. E.g. customer ledgers, and student databases.
Features of master file
1. The data stored in these files are permanent by nature
2. These files are updated only through recent transactions
3. This file stores a large amount of data

c. Reference Files: Reference files are the type of master file containing referential data. They contain data that are necessary to support data processing e.g. price lists, dictionary files, present value schedules, table of inventory codes or categories, lookup tables

Features of reference file
1. It is stable and permanent
2. It is data used for citation purposes.

Criteria for File Classification

1. How the file is to be used
2. How many records are processed each time the file is updated
3. whether the individual records need to be quickly accessible
4. nature of content
5. Organization method
6. Storage medium