Objectives: Introduction Over View of System Analysis and Design

Byte:- It is the smallest addressable unit in computer. A byte is a set of 8 bits and represents a character.
Element:- It is a combination of one or more bytes. It is referred to as afield. Afield is actually a physical space on tape or disk. A roll number, age, name of employee etc. are examples of it.
Record: - The elements related to are combined into a record. An employee has a record with his name, designation, basic pay, allowances, deductions etc. as its fields. A record may have a unique key to identify a record e.g. employee number. Records are represented as logical & physical records. A logical record maintains a logical relationship among all the data items in the record. It is the way the program or user sees the data. In contrast a physical record is the way data are recorded on a storage medium.
File: - It is a collection of similar records. The records will have the same fields but different values in each record. The size of a file is limited by the size of memory available.
Database: - It is a set of interrelated files. The files in combination tend to link to a common solution. For example, a student attendance file, a student result file, a student admission file, etc. are related to academic software pertaining to students.

7.3 File Design

A file is organized to ensure that records are available for processing. It should be designed in the line with the activity and volatility of the information and the nature of the storage media and devices. Other considerations are (1) cost of file media (highest for disk, lowest for tape) (2) inquiry requirements (real – time versus batch processing) and
(3) file privacy, integrity, security, and confidentiality. There are four methods of organizing files sequential, indexed – sequential, inverted list and direct access. Each method is explained.

Download 0.94 Mb.

Share with your friends: