Programming. The Internet

PROGRAMMING AND GLOBAL COMPUTER NETWORKS

What is Web Programming? Programming is the art of telling a computer what to do. Programming is giving written instructions in a logical manner that the computer can understand. Essentially, you give the computer small steps of instructions, and the computer goes down the list, executing each one in order. Programming allows you to make new software and have the computer do new things. Web site programming is the same except you write applications or web pages that are used by a web browser.
Web Site Programming is the practice of writing applications that run on a web server and can be used by many different people. Many applications work really well as a web application. Some examples of popular web applications include Flickr, Gmail, and Google Maps. You are able to upload and view pictures, send email and lookup directions using these web applications and they are all made possible through web site programming. When you access your page with a browser, your web server will parse, or read through, your HTML page line by line and when it comes across a programming language, it will execute the code. For example, it writes out the current date on the page and then sends the page back
to your web browser. Your web browser just sees a normal web page with a date but the server will generate a different web page when it is loaded on a different date. Web site programming allows you to turn a simple, static HTML page into a dynamic, Web 2.0 masterpiece. It allows others to interact with your web site and use the application on any computer with Internet access. Web site programming is often easier than programming applications that will run directly on the computer. Essentially, if you want to make or edit anything dynamic on your website, such as a forum, a guestbook, or even a form submission, you will need to know how to do some web site programming.
All web programming is done with web programming languages. Just as there is a diversity of programming languages available and suitable for conventional programming tasks, there is a diversity of
languages available and suitable for Web programming. There is no reason to believe that any one language will completely monopolize the Web programming scene, although the varying availability and
suitability of the current offerings is likely to favor some over others.
These languages can include static technologies like HTML, XHTML, CSS, JavaScript, and XML. However, most web site programming is done using server-side web programming languages. This code runs on
the server and then gives static information back to the web browser.
The most popular web programming languages are: PHP, ASP.NET, Ruby on Rails, Perl, ASP classic, Python, and JSP. HTML (Hyper Text Markup Language) is the basic language understood by all WWW (World Wide Web) clients. HTML is a markup language rather than a complete programming language. An HTML document (program) is ASCII text with embedded instructions (markups) which affect the way the text is displayed. HTML is limited in its computational power. This is intentional in its design, as it prevents the execution of dangerous programs on the client machine. Given the diversity of operating systems and hardware platforms, currently in use on the Web, a great efficiency results from only dealing with a single form of an application. The success of HTML has proven this, and Java has seconded it. The ability to deliver a platform-independent application is of great appeal to developers, who spend a large portion of their resources developing and maintaining versions of their products for the different hardware/software platform combinations.
Viruses have proven that executing binary code acquired from an untrusted, or even moderately trusted, source is dangerous. Code that is downloaded or uploaded from random sites on the web should not be
allowed to damage the user’s local environment. Downloading binary code compiled from conventional languages is clearly unsafe, due to the power of the languages. Even if such languages were constrained to some ostensibly safe subset, there is no way to verify that only the safe subset was used or that the compiler used was trustworthy (after all, it is under someone else’s control). HTML proved that downloading source code in a safe language and executing it with a trusted interpreter was safe.

STAGES IN PROGRAMM

There are five stages in programming. First, the computations to be performed must be clearly and precisely defined. The over-all plan of the computations is diagramed by means of a so-called flow chart. The second stage is the actual coding. It is often best to write a code in terms of a symbolic language first, for then changes are easily made. Numbers are assigned to the symbols, and the final code is prepared. In the third stage some procedure is used to get the code into the memory of the computer. The fourth stage consists of debugging the code, i.e., detecting and correcting any errors. The fifth and final stage involves running the code on the computer and tabulating the results. In fact, it is well known that a single error in one instruction invalidates the entire code. Hence, programming is a technique requiring attention to details without losing sight of the over-all plan.

KINDS OF PROGRAMS

There are two main kinds of programs which are subdivided as well. They are control programs and system service programs.  There are some control programs to handle interruptions, I/O operations, transition between different jobs and different phases of the same job, initial program loading (IPL), and symbolic assignment of I/O devices. Actually, the control program consists of three components:

1. IPL Loader. When system operation is initiated, the hardware IPL reads in this program which then clears unused core storage to zeros, generally performs some housekeeping operations, and then reads in the Supervisor.

2. The Supervisor. It can handle execution of any I/O operations and can provide standard processing for all interrupts. It may also queue I/O operations so that the operation will start as soon as the required channel and device are free.

3. Job Control. This program senses and processes all cards; after the new job is loaded, it turns control over to the new job. This system of operation eliminates the necessity of operation intervention between jobs, something which is of importance on large computers where the average job time may be less than one minute.

System Service Programs are used to maintain the library; to place new programs into the library, to delete, replace, or change existing programs, to read programs from the library into memory, to link segments of programs written at different times into one program, etc. They are called Librarian and Linkage Editor.

What the Internet is

The Internet is an International computer Network made up of thousands of  networks linked together. All these computers communicate with one another; they  share data, resources, transfer information, etc. To do it they need to use the same  language or protocol: TCP / IP (Transmission Control Protocol / Internet  Protocol) and every computer is given an address or IP number. This number is a way to identify the computer on the Internet. 

 Getting connected

To use the Internet you basically  need a computer, the right  connection software and a modem to 
connect your computer to a telephone line and then access your ISP (Internet Service Provider).
The modem (modulator-demodulator) converts the digital signals stored in the  computer into analogue signals that can be transmitted over telephone lines. There are two basic types: external with a cable that is plugged into the computer via a USB port, and internal, an expansion card inside the computer. A PC card modem is a different, more versatile option for laptops and mobile phones.
At first most computers used a dial-up telephone connection that worked through the standard telephone line. Now a broadband connection, a high data transmission rate Internet connection, has become more popular: either ADSL (Asymmetric Digital Subscriber Line), which allows you to use the same telephone line for voice and fast access to the Internet, or cable, offered by most TV cable providers.
The basic equipment has changed drastically in the last few years. You no longer need a computer to use the Internet. Web TV provides email and access to the Web via a normal TV set plus a high-speed modem. More recently, 3 Generation mobile phones and PDAs, personal digital assistants, also allow you to go online with wireless connections, without cables. Telephone lines are not essential either. Satellites orbiting the earth enable your computer to send and receive Internet files. Finally, the power-line Internet, still under development, provides access via a power plug.

Components of the Internet

The Internet consists of many systems that offer different facilities to users. WWW, the World Wide Web, is a collection of files or pages containing links to other documents on the Net. It’s by far the most popular system. Most Internet services are now integrated into the Web.
Email, or electronic mail, for the exchange of messages and attached files. Mailing lists (or listservs) based on programs that send messages on a certain topic to all the computers whose users have subscribed to the list.
Chat and instant messaging, for real-time conversations; you type your messages on the keyboard.
Internet telephone is a system that lets people make voice calls via the Internet. Video conference is a system that allows the transmission of video and audio signals in real-time so the participants can exchange data, talk and see one another on the screen.
File Transfer Protocol (FTP), used to transfer files between computers. Newsgroups, where people send, read and respond to public bulletin board messages stored on a central computer.
TELNET, a program that enables a computer to function as a terminal working from a remote computer and so use online databases or library catalogues.

What the Web is

The World Wide Web, Web or WWW is a network of documents that works in a hypertext environment, i.e. using text that contains links, hyperlinks to other documents.The files, web pages, ar c stored in computers, which act as servers. Your computer, the client, uses a web browser, a special program to access and download them. The web pages are organized in websites, groups of pages located on the Web, maintained by a webmaster, the manager of a website.
The Web enables you to post and access all sorts of interactive multimedia information and has become a real information highway.

How to surf the Web

To surf or navigate the Web, access and retrieve web pages or websites, you need a computer with an Internet connection and a web browser. After you have launched it, you must type the website address or URL. (Uniform Resource Locator), which may look like this:

http://www.cup.org/education/sample.hfm
http:// indicates the type of protocol that the server and browser will use to communicate. Here it is Hypertext Transfer Protocol.
www. shows that it is a resource on the World Wide Web.
cup.org is the domain name of the web server that hosts the website. 
education is the path, the place where a web page is located.
sample.htm is the filename or name of a single web page.
The different parts arc separated by full stops (.) and forward slashes (/). When we say a URL, we say dot (.) and slash (/).

The most common types of Internet crimes

The Internet provides a wide variety of opportunities for communication and development, but unfortunately it also has its dark side. Crackers, or black-hat hackers, are computer criminals who use
technology to perform a variety of crimes: virus propagation, fraud, intellectual property theft, etc.
Internet-based crimes include scam, e-mail fraud to obtain money or valuables, and phishing, bank fraud, to get banking information such as passwords of Internet bank accounts or credit card details. Both
crimes use e-mails or websites that look like those of real organizations.
Crackers are a new type of criminals. Due to its anonymity, the Internet also provides the right environment for on-line harassment orabuse, mainly in chat rooms or newsgroups. Piracy, the illegal copying and distribution of copyrighted software, information, music and video files, is widespread. But by far the most common type of crime involves malware. Malware (malicious software) is software created to damage or alter the computer data or its operations.

These are the main types.
– Viruses are programs that spread by attaching themselves to executable files or documents. When the infected program is run, the virus propagates to other files or programs on the computer. Some
viruses are designed to work at a particular time or on a specific date, e.g. on Friday l3th. An e-mail virus spreads by sending a copy of itself to everyone in an e-mail address book.
– Worms are self-copying programs that have the capacity to move from one computer to another without human help, by exploiting security flaws in computer networks. Worms are self-contained and
don’t need to be attached to a document or program the way viruses do.
– Trojan horses are malicious programs disguised as innocentlooking files or embedded within legitimate software. Once they are activated, they may affect the computer in a variety of ways: some are
just annoying, others are more ominous, creating a backdoor to the computer which can be used to collect stored data. They don’t copy themselves or reproduce by infecting other files.
– Spyware, software designed to collect information from computers for commercial or criminal purposes, is another example of malicious software. It usually comes hidden in fake freeware or shareware applications downloadable from the Internet.
– Don’t open e-mail attachments from unknown people; always take note of the file extension.
– Run and update antivirus programs, e.g. virus scanners.
– Install a firewall, a program designed to prevent spyware from gaining access to the internal network.
– Make backup copies of your files regularly.
– Don’t accept files from high-risk sources.
– Use a digital certificate, an electronic way of proving your identity, when you are doing business on the Internet. Avoid giving credit card numbers.
– Don’t believe everything you read on the Net. Have a suspicious attitude toward its contents.