Given are the definitions of some important terms:
1) Field: This is an elementary data item characterized by its size, length and type.
For instance,
Name : a character type of size 10
Age : a numeric type
2) Record: This is a collection of associated fields that can be treated as a unit from an application viewpoint.
For example:
A university could employ a student record with the fields, namely, University enrolment no. and names of courses.
3) File: Data is organized for storage in files. A file is a collection of similar, associated records. It has an identifying name.
For instance, "STUDENT" could be a file containing student records for all the students in a university.
4) Index: An index file corresponds to a data file. Its records have a key field and a pointer to that record of the data file that has the similar value of the key field.
The data stored in files is accessed by software that can be divided into the following two categories:
i) User Programs: Usually these are written by a programmer to manipulate retrieved data in the manner attained by the application.
ii) File Operations: this deal along with the physical movement of data, in and out of files. User programs effectively employ file operations through appropriate programming language syntax The File Management System handle the independent files and behaves as the software interface among the user programs and the file operations.
File operations can be categorized as
- CREATION of the file
- INSERTION of records into the file
- UPDATION of earlier inserted records
- RETRIEVAL of earlier inserted records
- DELETION of records
- DELETION of the file.