Computer Data Processing and Representation 4 1226486685302309 8

8/2/2019 Computer Data Processing and Representation 4 1226486685302309 8

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Data HierarchyListed here in ascending order of complexity are the componentsof the data hierarchy in an information system.

Bit:- The term is bit is short form for binary digit. Itcan assume either of two possible states and

therefore can represent either 0 or 1. In secondarystorage a bit is used to represent data throughpositive or negative polarity of an electrical charge ona magnetic recording medium such as tape or disk.Semi conductor storage is usually used for primarystorage. In semiconductor storage a bit is represented

by an electrical circuit that is either conducting or notconducting electricity.


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F

ield or Item:The next level in the data hierarchy is a

field or Item of data. A field or item of

data is one or more bytes that containdata about an attribute of an entity in theinformation system. An entity in a payrollsystem is an individual employee.Attributes are the employees name, pay

rate, and so on. The basic pay is a field oritem of data.


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Record:

A record is a collection of fields relating to a specific entity.For example, a payroll record contains fields

of data relating to a specific employee. An analogy can bemade between a computer-based record and an individual

folder in a manual file. A folder in a payroll file may containmuch the same information as a record in a computer-basedpayroll file. The field that identifies a record from all other

records in a file is the record key. For example, therecord key in a payroll record is usually the employeesprovident fund number or social security number becauseit is different for each employee.


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File: A file is a collection of related records. For example, thecollection of payroll records for all employees in a company is

a payroll file. The concept of a computer file is very similar toa manual file in a filing cabinet.

Data Base: A database consists of all the files of anorganization, structured and integrated to facilitate update ofthe files and retrieval of information from them. The term has

often been used rather loosely. Technically a databaseconsists of those files that are part of a data basemanagement system. However, database is often used to referto all the files of an organization.All this is called as data hierarchy because databases arecomposed of files, files are composed of records, records are

composed of filed, fields composed of data bytes, and finallydata bytes are a group of bits. This is very well a hierarchicalstructure.


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Indexed Sequential Access File:

The most common technique for accessing disk records directly is withthe use of an index. During the creation of records, the computer usesfile-handling programmed routines to establish an index on the diskitself. The index indicates where each record is located. The concept issimilar to that of the index found at the end of book, which specifiesthe page where each item of information can be located. The disk indexindicates the locations (i.e. track and sector) of each record and wherea particular record can be found. A key data field in each record must

be indicated by the programmer, which is used by the computer as thebasis for establishing, address information in the index.For example, if a payroll file is stored on a disk. To access any

articular record, the user need only supply a particular key datafield, such as EMPLOYEE CODE or whatever has been defined atthe time of programming. The computer then looks up thecorresponding disk location for that particular record in the indexand seeks that record directly.


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Preparation of Source Document: The firststep is to obtain the relevant facts and

figures and to set these out on sourcedocuments, for example, in a population survey,the name, address, age, sex, occupation, etc.,must be first written down on to a surveysheet or some other document. These

documents may be so designed thatinformation is recorded in the required order.

Input of Data: Once the data has beenextracted from the source document, it must

then be transferred into some form suitablefor data entry into the computer so that

processing can take place. Themethod will depend upon the input

media and the devices.


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Manipulation of Data: Information, inputs forprocessing may have to be classified or sorted. It isThis form of operation, or data manipulation, ratherthan pure computation, with which data processing ismainly concerned. For example, in the populationsurvey we may want to classify people by occupation orby age. We may wish to sort lists on alphabetical orderor in any other order. We may require employees to begrouped by departments for a pay roll program. All

these forms of data manipulation will produce results,which can be organized in the form of summaries.

Output of Information: The objective of results orsummaries is to provide meaningful information toManagers, Accountants, etc., and carefulconsideration, therefore, should be given to the

presentation of results so that they can beunderstandable easily and quickly.


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Data Storage: In most cases, the results ofprocessing are retained for future use orreference. In many cases, it may benecessary after updating, to compare thelatest figures with the previous figures,perhaps, over different periods of time. Thismeans that data processing installationsrequire a great deal of secondary storage

space to store all the programs and thedifferent sets of data.


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Types of Data ProcessingBasically there are two types of data processing

Batch Processing - With batch processing,changes and queries to file are stored for aperiod of time, and then a processing run ismade periodically to update the file and to

produce responses to the queries. Batch runscan be made on a scheduled basis, such as daily,weekly, or-monthly, or they can be made on anas required basis. Examples of batch processinginclude generation of mark-sheets of students.

Mark-sheets and results of school examinationsare given to students only at the end ofan academic year. So, a programmercan develop a program for this and theresults can he printed at the required

time.


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Online or Immediate ProcessingIn immediate processing, transactions are processed to update

the file immediately or shortly after a real-world event occurs.Information processing applications that use immediateprocessing are often called real time application. A real timeapplication can immediately capture data about ongoing events orprocesses and provide the information necessary to manage them.An airline-reservation system is an example of a real timeapplication.

Real time systems must have real time files that are updatedimmediately after the event occurs. Consequently, at any point intime, the data in real time files should accurately reflect thestatus of the real world variables they represent. For example,when a customer reserves a seat on an airline flight, thereservations agent keys in that fact and the inventory of nonreserved seats on the flight is immediately changed to reflectone less available seat. Immediate processing requires direct-access files, since immediate processing with sequential fileswould be impractical because of the time required to search for

individual records. Batch processing, on theother hand, can occur with either sequentialor direct access files.

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Computer Data Processing and Representation 4 1226486685302309 8