Data Processing Concept-2

2.7 The Data Processing Cycle

The data processing activities described above are common to all data processing systems from manual to electronic systems. These activities can be grouped in four functional categories, viz., data input, data processing, data output and storage, constituting what is known as a data processing cycle.

(i) Input

The term input refers to the activities required to record data and to make it available for processing. The input can also include the steps necessary to check, verify and validate data contents.

(ii) Processing

The term processing denotes the actual data manipulation techniques such as classifying, sorting, calculating, summarizing, comparing, etc. that convert data into information.

(iii) Output

It is a communication function which transmits the information, generated after processing of data, to persons who need the information. Sometimes output also includes decoding activity which converts the electronically generated information into human-readable form.

(iv) Storage

It involves the filing of data and information for future use. The above mentioned four basic functions are performed in a logical sequence as shown in Fig. 2.3 in all data processing systems. 

2.8 Computer Processing Operations 

A computer can perform only the following four operations which enable computers to carry out the various data processing activities we have just discussed.

(a) Input/Output operations

A computer can accept data (input) from and supply processed data (output) to a wide range of input/output devices. These devices such as keyboards, display screens, and printers make human-machine communication possible.

(b) Calculation and text manipulation Operations

Computer circuits perform calculations on numbers. They are also
capable of manipulating numerics and other symbols used in text with
equal efficiency.

(c) Logic/Comparison Operations

A computer also possesses the ability to perform logic operations. For example, if we compare two items represented by the symbols A and B, there are only three possible outcomes. A is less than B (A<B); A is equal to B (A=B): or A is greater than B (A>B). A computer can perform such comparisons and the, depending on the result, follow a predetermined path to complete its work. This ability to compare is an important property of computers.

(d) Storage and Retrieval Operations

Both data and program instructions are stored internally in a computer. Once they are stored in the internal memory, they can be called up quickly or retrieved, for further use.

2.9 Data Processing System

The activity of data processing can be viewed as a "system". According to James O'brien a system can be defined as "a group of interrelated components that seeks the attainment of a common goal by accepting inputs and producing outputs in an organised process". For example, a production system accepts raw material as input and produces finished goods as output. Similarly, a data processing system can be viewed as a system that uses data as input and processes this data to produce information as output.

There are many kinds of data processing systems. A manual data processing system is one that utilizes tools like pens, and filing cabinets. A mechanical data processing system uses devices such as typewriters, calculating machines and book-keeping machines. Finally, electronic data processing uses computers to automatically process data.

2.10 Data Organisation

Having discussed the Data Processing Cycle (also called Information Processing Cycle) and the components of a computer, we will now describe how data is organised before processing on a computer. Data can be arranged in a variety of ways, but a hierarchical approach to organisation is generally recommended.

Data Item

A data item is the smallest unit of information stored in computer file. It is a single element used to represent a fact such as an employee's name, item price, etc. In a payroll application, the employee number 170 is a data item. PANKAJ the name is a data item.

Field

Data items are physically arranged as fields in a computer file. Their length may be fixed or variable. Since all individuals have 3 digit employee numbers, a 3-digit field is required to store the particular data.

Hence, it is a fixed field. In contrast, since customer's name vary considerably from one customer to another, a variable amount of space must be available to store this element. This can be called as variable field.

Record

A record is a collection of related data items or fields. Each record normally corresponds to a specific unit of information. For example, various fields in the record, illustrated in Fig. 2.4 are employee number, employee's name, basic salary and house rent allowance. This is the data used to produce the payroll register report. The first record contains all the data concerning the employee PANKAJ. The second record contains all the data concerning the employee REKHA. Each subsequent record
contains all the data for a given employee. It can be seen how each related item is grouped together to form a record.

File

The collection of records is called a file. A file contains all the related records for an application. Therefore, the payroll file shown in Fig. 2.5 contains all records required to produce the payroll register report. Files are stored on some medium, such as floppy disk, magnetic tape or
magnetic disk.

Database

The collection of related files is called a database. A database contains all the related files for a particular application.

2.11 Variable and Fixed Length Records

Records can be of fixed or variable length as depicted in Fig. 2.5

Fixed Length Records

In this case, all the records in a file have the same number of bytes. Such a file is called a flat file. If all the records are expected to contain essentially the same quantity of data, then fixed length records are used.

Variable Length Records

In this case, records vary in length. Use of variable length records conserves storage space when the quantity of information, of various records in a file, differs significantly.

2.12 Logical Versus Physical Record

A logical record contains all the data related to a single entity. It may be a payroll record for an employee or a record of marks secured by a student in a particular examination. A physical record refers to a record whose data fields are stored physically next to one another. It is also the amount of data that is treated as a single unit by the input-output device. Portions of the same logical record may be located in different physical records or several logical records may be located in one physical record. For example, in case of magnetic tape, number of logical records are stored in the form of a block to increase the data transfer speed and this block is referred to as a physical record as shown in Fig.