MBA management

Computer Systems, Files and Database topics:

CONCEPT OF COMPUTER FILES


A File can be defined as a collection of related information. Just as there are files (Accounts Leger and Kardex Cards) in manual systems, there are files in computer system too; but the media is usually magnetic so that the computer can itself read the files. Computer performs arithmetic computations and it is extremely fast in this function. Upon reading the files and the details of transactions it can update the file. Besides it can produce such output as replenishment orders in the works and vendors and inventory control application and pay slips in a payroll application. Data files used in business can be divided into seven types.

1) Master Files
A Master file contains relatively permanent records for identification and summarizing statistical information. A product file, customer file and employee file are examples of master files. The descriptive information in a master file includes such items as product code, descriptions, specifications, etc. Statistical information, in a customer master file, contains amount outstanding, age of outstanding etc.

2) Transaction Files
Transaction files are created from source documents used for recording events or transactions. These are detail files, and thee information is used for updating the master files. If the processing is of the batch type, the transactions are accumulated for a period and a transaction file is created at the end of the period. The typical source documents from which transaction files are purchase orders, Job Cards, Invoices etc.

3) Reference Files
These files contain keys of records in order files. In order to retrieve a record from a file, the reference file is first searched to find out in which file a record can be located.

4) Table Files
These are in the nature of catalogues or price lists.
5) Report Files
A report file is created from records in other files in a meaningful and concise from. A sales performance report and a report on materials rejected are examples of report files.

6) Historical Files
These contain statistical information of the past periods. These files are used to analyze trends or make comparisons of one period with another and so on.

7) Back-up Files
These are copies of currently used master files kept in the computer library as a measure of security.

File Contents


As the lowest level, many modern operating systems consider files simply as an on-dimensional sequence of bytes. At a higher level, where the content of the file is being considered, these binary digits may represent integer values, text characters, image pixels, audio or anything else. It is up to the program using the file to understand the meaning and internal layout of information in the file and present it to a user as more meaningful information (like text, images, sounds, or executable application programs).

At any instant in time, a file might have a size, normally expressed as number of bytes that indicates how much storage is associated with the file. In most modern operating systems the size can be any non-negative whole number of bytes up to a system limit. However, the general definition of a file does not require that its instant size has any real meaning, unless the data within the file happens to correspond to data within a pool of persistent storage.

For example, the file to which the link/bin/Is points in a typical Unix- like system probably has a defined size that seldom changed. Compare this with/dev/null. This is a file, but its size may be open to question.

Information in a computer file can consist of smaller packets of information (often called “records” or “lines”) that are individually different but share some trait in common. For example, a payroll file might contain information concerning all the employees in a company and their payroll details: each record in the payroll file concerns just one employee, and all the records have the common trait of being related to payroll—this is very similar to placing all payroll information into a specific filing cabinet in an office that does not have a computer. A text file may contain lines of text, corresponding to printed lines on a piece of paper. Alternatively, a file contains an arbitrary binary image or it may contain an executable.

The way information is grouped into a file is entirely up to the person designing the file. This has led to a plethora of more or less standardized file structures for all imaginable purposes, from the simplest to the most complex. Most computer files are used by computer programs. These programs create, modify and delete files for their own use on as-needed basis. The programmers who create the programs decide what files are needed, how they are to be used and (often) the names of those files.

In some cases, computer programs manipulate files that are made visible to the computer user. For example, in a word-processing program, the user manipulates document files that the user personally names. The content of the document file is arranged in a way that the word-processing program understands, but the user chooses the name and location of the file and provides the bulk of the information (such as words and txt) that will be stored in the file.

Many applications pack all their data files into a single file, using internal markers to discern thee different types of information contained within. Files on a computer can be created, moved, modified, grown, shrunk and deleted. In most cases, computer programs that are executed on the computer, handle these operations, but the user of a computer can also manipulate files if necessary. For instance, Microsoft Word files are normally created and modified by the Microsoft Word program in response to user commands, but the user can also move, rename, or delete these files directly by using a file manager program such as Windows Explorer ( on Windows computers).

In Unix-like systems, user-space processes do not normally deal with files at all; the operating system provides a level of abstraction which means that almost all interaction with files from user-space is through hard links. Hard links allows a name to be associated with a file (or they can be anonymous and therefore temporary); files do not have names in the OS. For example, a user-space program cannot delete a file; it can delete a link to a file (for example, using the shell commands rm or mv or, in the anonymous case, simply by exiting), and if the Kernel determines that there are no more existing links to the file, it may then delete the file. In fact, it really is only the kernel that deals with files, but it serves to handle all user=space interaction with (virtual) files in a manner that is transparent to the user-space programs.

Identifying and organizing files


Files and folders are arranged in a hierarchy in modern computer systems. Files are typically accessed using names (filenames). In some operating systems, the name is associated with the file itself. In others, the file is anonymous, and is pointed to by links that have names. In the latter case, a user can identify the name of the link with the file itself, but this is a false analogue, especially where there exists more than one link to the same file.

Files (or links to files) can be located in directories. However, more generally, a directory can contain either a list of files or a list of links to files. Within this definition, it is of paramount importance that the term “file” includes directories. This permits the existence of directory hierarchies, i.e., directories containing subdirectories. A name that refers to a file within a directory must be unique. In other words, there must be no identical names within a directory. However, in some operating systems, a name may include a specification of type that mans a directory can contain an identical name for more than one type of object such as a directory and a file.

In environments in which a file is named, a file’s name and the path to the file’s directory must uniquely identify it among all other files in the computer system-no two files can have the same name and path. Where is anonymous, names references to it will exist within a namespace. In most cases, any name within the namespace will refer to exactly zero or one file. However, any file may be represented within any namespace by zero, one or more names.

Any string of characters may or may not be a well-formed name for a file or a link depending upon the context of application. Whether or not a name is well-formed depends on the type of computer system being used. Early computers permitted only a few letters or digits in the name of a file, but modern computers allow long names( some up to 255 characters)containing almost any combination of Unicode letters or Unicode digits, making it easier to understand the purpose of a file at a glance. Some computer systems allow file names to contain spaces: others do not. Case- sensitively and allow user-level applications to create files whose names differ only in the case of characters. Microsoft Windows supports multiple file systems, each with different policies regarding case-sensitivity. The common FAT file system can have multiple files whose names differ only in case if the user uses a disk editor to edit the file names in the directory entries. User applications, however, will usually not allow the user to create multiple files with the same name but differing in case.

Most computers organize files into hierarchies using folders, directories, or catalogs. The concept is the same irrespective of the terminology used. Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as subfolders. Subfolders can contain still more files and folders and so on, thus building a tree- like structure in which one “ master folder”(or “root folder”-----the name various from one operating system to another) can contain any number of levels of other folders and files. Folders can be named just as files can (except for the root folder, which often does not have a name). The use of folders makes it easier to organize files in a logical way.

When a computer allows the use of folders, each file and folder has not only a name of its own, but also a path, which identifies the folder or folders in which a file or folder resides. In the path, some sort of special character-such as a slash-is used to separate the file folder names. For example, in the illustration shown in this article, the path/Payroll/Salaries / Managers uniquely identifies a file called Managers in a folder called Salaries, which in turn is contained in a file called Payroll. The folder and file names are separated by slashes in this example: the topmost or root folder has no name, and so the path begins with a slash (if the root folder had a name, it would precede this first slash).

Many (but not all) computer systems use extensions in file names to help identify what they contain, also known as the file type. On Windows computers, extensions consist of a dot (period) at the end of a file name, followed by a few letters to identify the type of file. An extension of .txt identifies a text file; a .doc extension identifies any type of document or documentation, commonly in the Microsoft Word file format; and so on. Even when extensions are used in a computer system, the degree to which the computer system recognizes and heeds them can vary; in some systems, they are required, while in other systems, they are completely ignored if they are present.

Protecting Files


Many modern computer systems provide methods for protecting files against accidental and deliberate damage. Computers that allow for multiple users implement file permissions to control who may or may not modify, delete, or create files and folders. A given user may be granted only permission to modify a file or folder, but not to delete it; or a user may be given permission to create files or folders, but not to delete them. Permissions protect against unauthorized tampering or destruction of information in files, and keep private information confidential by preventing unauthorized users from seeing certain files.

Another protection mechanism implemented in many computers is a read- only flag. When this flag is turned on for a file (Which can be accomplished by a computer program or by a human user),the file can be examined, but it cannot be modified. This flag is useful for critical information that must not be modified or systems also include a hidden flag to make certain files invisible; this flag is used by the computer system to hide essential system files that users should not alter.

DATABASE


A computer database relies on software to organize the storage of data. This software is known as a database management system (DBMS).Database management systems are categorized according to the database model that they support. The model tends to determine the query languages that are available to access the database. A great deal of the internal engineering of a DBMS, however, is independent of the data model, and is concerned with managing factors such as performance, concurrency, integrity, and recovery from hardware failures. In these areas there are large differences between products.

Database files have data elements stored in database file organization formats. The data base crated in such a way so as to balance the data management objectives of speed, multiple access paths, minimum storage, program-data independence and preservation of data integrity. Different database systems have different ways of representing data physically on disk. The physical representations can b complex and generally the user is not concerned about them. Basically, the DDMS tries to store data in ways that facilitate rapid access while economizing on storage. The user is only concerned with the logical view of the data that is how the user sees the relationship among data. For Instance, a bank manager should know that the data base contains the name, address, and phone numbers of customers, as well as recent savings, cheques loans histories etc. Exactly how these data elements are physically stored is not particularly important to the manager. Physical data descriptions are of concern to the MIS department which must select a data base system that meets the needs of users at a reasonable cost.

A Relational Database Management System (RDBMS) implements the features of the relational model outlined above. In this context, Date’s “ Information principle” states: “the entire information content of the database is represented in one and only one way, namely as explicit values in column positions (attributes) and rows in relations (tuples). Therefore, there are no explicit pointers between related tables.

DATABASE MANAGEMENT SYSTEM


A Database Management System is a set of system software programs that manages the data base files. The Data Base Management System accesses the files, updates the records, and retrieves data as requested. The DBMS has the responsibility for data security which is vital in a data base environment since data base is accessed by many users.

Database Management System may perform the following tasks:

1) Suppose an application program such as payroll is being executed. The program requires some data from the database and contains a command that will cause the needed data elements to be retrieved. The control unit of thee Central processing Unit causes each instruction of the application program to be executed in sequence. When the data manipulation language command is reached, thee control passes from the application program to the DBMS.

2 ) The DBMS verifies that the data requested has been previously defined in the user’s sub scheme, and that access should be permitted. The DBMS used its access path mechanisms to identify where the needed elements are located in the data base.

3) The DBMS requests the operating system to execute an input operation.

4) The operating system causes the data to be accessed, read, and transmitted to a buffer storage area in primary storage. This is a special buffer storage used by the DBMS. Control passes from the operating system back to the DBMS.

5) The DBMS transfers the data from the buffer storage to the input area used by the application program.

6) The DBMS provides status information to the application program, such as record found or record not found.

7) The application program processes the data.

OPERATING SYSTM SOFTWARE


The operating system software provides for several other functions including:

• System tools (programs) used to monitor computer performance, debug problems, or maintain parts of the system.

• A set of libraries or functions which programs may use to perform specific tasks especially relating to interfacing with computer system components.

As mentioned previously, an operating system is a computer program. Operating systems are written by human programmers who can make mistakes. Therefore there can be errors in the code even though there may be some testing before the product is released. Some companies have better software quality control and testing than others so you may notice varying levels of quality from operating system to operating system. Errors in operating systems cause three main types of problems.

• System crashes and instabilities-These can happen due to a software bug typically in the operating system, although computer programs being run on the operating system can make the system more unstable or may even crash the system by themselves. This varies depending on the type of operating system. A system crash is the act of a system freezing and becoming unresponsive which would cause the user to need to reboot.

• Security flaws-Some software errors leave a door open for the system to be broken into by unauthorized intruders. As these flaws are discovered, unauthorized intruders may try to use these to gain illegal access to your system. Patching these flaws often will help keep your computer system secure. How this is done will be explained later.

• Sometimes errors in the operating system will cause the computer not to work correctly with some peripheral devices such as printers.

APPLICATION PACKAGES


Application Packages or just software is a general term used to describe a collection of computer programs, procedures and documentation that perform some tasks on a computer system.

Application packages are software developed by programmers to the achievement of specific task in the day to day life. Application Software is meant for the End Users who are not having sufficient programming knowledge. Application Packages are written using high level languages and are very effective in solving the requirement of thee Users. Application packages are also readily available for standard applications such documentation, Office Automation, accounting etc.

Application packages are developed with accuracy and according the complete requirement of the Users for accomplishing their objectives. Application packages are useful for the users in many ways.

Application packages are readily available in the market supplied by the various software vendors.

The main features of an Application Packages are as follows:

1. It is user friendly
2. It is cost effective
3. It can be implemented and maintained easily
4. It satisfies all requirements of the users
5. It has all procedures and regulations according to the objective
6. It is also readily available sometimes
7. It is prepared to solve the day to day problems

TYPES OF APPLICATION PACKAGES


There are different types of Application packages which are implemented in various sectors. All the areas of business are governed by Application Packages. The Application Packages are used for the following areas of Business
1) Accounting
2) Office automation
3) Administration
4) Human Resources Development
5) Inventory Control

USER WRITTEN PROGRAMS


User written programs are small programs written by computer users to solve small problems. A user may write small programs using various programming techniques to do some routine programs. For e.g., under Microsoft Excel there is an option called Macro. The user creates a Macro to perform a sequence of operations which are run regularly. Users with knowledge about the working of computers generated small routines or programs to solve the day to day problems are called as user written programs.

The main features of User written Programs are as follows
1) They are small programs or Techniques
2) They are developed by computer users
3) They are flexible and can be changed according to the situation
4) They are effective in solving small problems
5) They developed by the users with lesser amount duration

COMMUNICATION AND NETWORKING TERMINOLOGIES INTERNET


A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network.

WORLD WIDE WEB


The World Wide Web (commonly abbreviated as “the Web”) is a system of interlinked hypertext documents accessed via the Internet. With a Web browser, one can view Web pages that may contain text, images, videos, and other multimedia and navigate between them using hyperlinks. Using concepts from earlier hypertext systems, the World Wide Web was started in 1989 by the English physicist Sir Tim Berners-Lee, now the Director of the World Wide Web consortium, and later by Robert Cailliau, a Belgian computer scientist, while both were working at CERN in Geneva, Switzerland. In 1990, they proposed building a “web of nodes” storing “hypertext pages” viewed by “browsers” on a network, and released that web in December. Connected by the existing Internet, other websites were created, around the world, adding international standards for domain names & the HTML language. Since then, Berners-L has played an active role in guiding the development of web standards (such as the markup languages in which Web pages are composed), and in recent years has advocated his vision of a Semantic web.

The World Wide Web enabled the spread of information over the Internet through an easy-to-use and flexible format. It thus played an important role in popularizing use of the Internet. Although the two terms are sometimes conflated in popular use, World Wide Web is not synonymous with Internet.

ELECTRONIC MAIL (EMAIL)


Electronic mail, often abbreviated as mail or e–mail, is a method of exchanging digital messages, designed primarily for human use.

An electronic mail message consists of two components, the message header, and the message body, which is the email’s content. The message header contains control information, including, minimally, an originator’s email address and one or more recipient addresses. Usually additional information is added, such as a subject header field.

The foundation for today’s global Internet e-mail service was created in the early ARPANET and standards for encoding of message were proposed as early as, for example, in 1973 ( RFC 561).An e-mail sent in the early 1970s looked very similar to one sent on the Internet today. Conversion from the ARPANET to the Internet in the early 1980 produced the core of the current service.

Network-based email was initially exchanged on thee ARPANET in extensions to the File Transfer Protocol (FTP), but is today carried by the Simple Mail Transfer protocol (SMTP), first published as Internet Standard 10 (RFC 821) in 1982. In the process of transporting email message between systems, SMTP communicates delivery parameters using a message envelope separately from the message (headers and body) itself.

Originally a text –only communications medium, email was extended to carry multi-media content attachments, which were standardized in 1996 with RFC 2045 through RFC 2049, collectively called, Multipurpose Internet Mail Extensions (MIME).

E-mail systems are based on a store-and-forward model in which e-mail computer server systems accept, forward, deliver and store messages on behalf of users, who only need to connect to the e-mail infrastructure, typically an e-mail server, with a network-enabled device (e.g., a personal computer) for the duration of message submission or retrieval. Rarely is e-mail transmitted directly from one user’s device to another’s.

HYPERTEXT


Hypertext is text, displayed on a computer, with references (hyperlinks) to other text that the reader can immediately access, usually by a mouse click or keypress sequence. Apart from running text, hypertext may contain tables, images and other presentational devices. Other means of interaction may also be present e.g., a bubble with text may appear when the mouse hovers over a particular area, a video clip may be started and stopped, or a form may be filled out and submitted.

WIRELESS NETWORKING


Wireless network
Refers to any type of computer network that is wireless, and is commonly associated with a telecommunications network whose interconnections between nodes is implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or “layer” of the network.

MODEM
Data communication is a communication unit which converts a digital computer signal into an analog telephone signal. Modems are used for handling data streams from a peripheral device to the Central Processing Unit and vice versa through the common carrier network. Modems are required to tele- communicate computer data with ordinary telephone lines because computer data is in digital form but telephone lines are analogue forms. Modems are built with different ranges of transmission speeds.

MULTIPLEXER
Multiplexer is a device which enables several devices to share one communication line. The Multiplexer scans each device to collect and transmit data on a single line to the Central Processing unit. It also communicates transmission from CPU to the appropriate linked to the Multiplexer. The devices are pooled and periodically asked whether there is any data to transmit.

BRIDGES
The main task of a bridge computer is to receive and pass from one Local Area Network to another. In order to transmit this data successfully, the bridge magnifies the data transmission signal. This means that the bridge can act as a repeater as well as a link.

REPEATERS
Repeaters are devices that solve the snag of snag of signal degradation which results as data is transmitted along the various cables. What happens is that the repeater boosts or amplifies the signal before passing it through to the next section of cable.

SWITCHES AND ROUTERS
Switches and Routers are hardware devices used to direct messages across a network. Switches create temporary point to point links between two nodes on a network and send all data along that link. Router computers are similar to bridges but have the added advantage of supplying the user with network management utilities. Router helps administer the data flow by means of redirecting.

PROGRAMMING CONCEPT


Programming Concept refers to the way of preparing a program or a method of creating or writing a program. Programing concept refers to the application of various methods and various techniques for creating a computer program. The computer programming involves various methods which are discussed as follows:

1) Program Design
Program Design is the first stage of creating a computer program. Under this stage, the programmer will analyze the various designs of programming and selects the appropriate design which will be effective for the targeted program. Program Design should be made carefully after considering the various factors such as internal and external factors.

2) Program Analysis
Program Analysis refers to the analytical stage of programming. Under this stage the various programming methods are analyzed with reference to the current programming technique. Program Analysis is an analytical measure taken by the programmer for constructing the program which should be suitable for the demanding situation.

3) Algorithm
Algorithm refers to thee step by step representation of the computer program. Algorithm gives a better idea of the program to the programmer. Algorithm is a technique used by the programmer to break the program into step by step operation.

4) Flow charting
Flow chart refers to the graphical representation of the various steps of the programming. Flowcharts refer to the tool used by the programmer to study the various steps, condition of the program. There are several types of flowcharts such as system flowcharts, runway flowcharts, program flowcharts etc.

5) Program coding
Program Coding refers to the preparation of program codes by the programmer. The programmer writes the appropriate coding for the execution of the program. The programmer should avoid syntax and logical errors under this stage. Program codes are usually written in high level languages.

6) Program Debugging
Debugging refers to the process of finding out the errors in the program. Programs are debugged using specialized software to remove the errors which are known as bugs. Under this stage, the various errors such as syntax errors and logical errors are removed from the program.
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Review Questions
  • 1. Discuss the concepts of computer files and explain their contents.
  • 2. What is a database? What is the database management systems. Discuss in detail.
  • 3. What is an operating system and software? What is an application package? What are the different types of application packages?
  • 4. What is a world wide web? What is an electronic mail? Describe them in detail.
  • 5. What are the different program concepts?
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