WWW (World Wide Web) is an information "spider web" attached to the Internet and covering the whole world. It embeds countless information in the form of hypertext, including bright pearls and, of course, rotten garbage. Some people call it the World Wide Web, others call it the World Wide Web, or simply the Web (the Chinese translation of WWW is the "World Wide Web" suggested by the National Committee for the Examination and Approval of Scientific and Technological Terminology). WWW is the most popular, popular and up-to-date information retrieval service system on the Internet. It connects all the existing resources on the Internet, so that users can provide hypertext media resource documents on all the sites with WWW servers on the Internet. This is because WWW can seamlessly integrate all kinds of information (still images, text sounds and audio-visual). WWW not only provides fast information search on the graphical interface, but also can connect with other servers on the Internet through the same graphical interface (GUI).
Because WWW provides people all over the world with the means to find and share information, it can also be regarded as a collection of information that all kinds of organizations, scientific research institutions, universities and companies in the world are keen on research and development. It is based on Internet query. Information publishing and management system is a dynamic multimedia communication format for people to interact. Its formal expression is: "the original protocol of wide-area hypermedia information retrieval, the purpose of which is to access massive documents." What WWW has achieved is to provide a compatible means for users on the computer network to access various media in a simple way. It is the first truly global hypermedia network, which has changed the way people observe and create information. As a result, the research, development and use of WWW have quickly set off a huge upsurge all over the world.
WWW was born in the Internet and later became a part of it. Today, the World Wide Web is almost synonymous with the Internet. Through it, everyone who joins it can reach every corner of the world in an instant, just plug in a telephone line (maybe your laptop or your mobile phone) on your PC, and the global information is at your fingertips!
WWW doesn't actually exist anywhere in the world. In fact, users of WWW give it new meanings every day. In the Internet society, citizens (including institutions and individuals) embed all kinds of information they need to disclose into the WWW in the form of homepages, which include graphics, sounds and other media besides words. From all kinds of job advertisements to electronic bibles, it can be said that it is all-encompassing and ubiquitous. The homepage is published on the Web, mainly in the form of some HTML text (HTML is Hypertext Markup Language).
Since the 1940s, people have always dreamed of having a worldwide information base. In this database, data can not only be accessed by people all over the world, but also be easily linked to information in other places, so that users can obtain important information conveniently and quickly. It triggered the fifth information revolution.
With the rapid development of science and technology, this dream has become a reality. The most popular system used at present is called WWW. Its formal definition is "WWW is a wide-area hypermedia information retrieval initiative, which provides universal access to the world's documents." In short, WWW is an Internet-based computer network, which allows users to access information from one computer to another through the Internet. Technically speaking, the World Wide Web is a collection of clients and servers that support WWW protocol and Hypertext Transfer Protocol (HTTP) on the Internet. Through it, you can access hypermedia files all over the world, including words, graphics, sounds, animations, databases and various softwares.
Theoretically, the World Wide Web includes the whole Internet world of more than 200 million people, including all websites, gopher information stations, FTP files, Telnet public access accounts, news discussion forums and Wais databases. Therefore, the World Wide Web can be said to be the largest electronic information world in the world today, and the World Wide Web can be regarded as synonymous with the Internet. In fact, what we usually call "surfing the Internet" actually refers to connecting to the World Wide Web. WWW is the abbreviation of World Wide Web, and it can also be abbreviated as Web, and its Chinese name is World Wide Web.
The World Wide Web is called the information network because its resources can be interconnected. At present, there are about tens of thousands of websites in the world, and each website can be connected with other websites through hyperlinks. Anyone can design their own homepage, put a website on the homepage, and then generate a link on your homepage to connect other people's homepages or other websites. Other people can also connect to your home page or your website, and the whole information network is thus woven into a huge global information network. This chapter will briefly introduce some concepts of the World Wide Web: client, server, protocol and so on. In this chapter, we will also learn about the history and development of the World Wide Web.
Client and server
Although client, server and protocol are simple concepts, it is more difficult to describe them than to understand them.
A client is a program that needs something, while a server is a program that provides something. A client can request from many different servers. Servers can also provide services to many different clients. Usually, the client starts a conversation with the server. Servers are usually automated programs that wait for requests from clients. The client usually runs as a request from the user or from every program similar to the user. A protocol is a definition of various methods for a client to request a server and how the server responds to the request. WWW client can also be called browser.
The usual clients on the World Wide Web mainly include Lynx, Mosaic, Netscape and so on. The usual servers come from CERN, NCSA and Netscape. Let's look at the specific tasks of clients and servers in the Web.
In the Web, the client's task is:
1. Helps you make a request (usually launched when you click the link point).
2. Send your request to the server.
3. Report the requested results to you by correctly decoding the direct image, submitting the HTML document and transferring various files to the corresponding "viewer".
Viewer is a program that can be called by WWW clients to present specific types of files. When a sound file is viewed and downloaded by your WWW client, it can only be "observed" by some programs (such as "media player" under Windows).
Generally speaking, WWW clients can make requests not only to Web servers, but also to other servers (such as Gopher, FTP, news and mail).
The tasks of the Web server are:
1. Accept the request
2. Check the legality of the request, including security screening.
3. Obtain and make data according to the request, including Java scripts and programs, CGI scripts and programs, set appropriate MIME types for files, and pre-process and post-process the data.
4. Send the information to the requesting client.
The network has a protocol called "stateless". This is because the server forgot to interact after sending a reply message to the client. In the "stateful" protocol, the client and the server must remember a lot of information about each other and their various requests and responses.
Web is an easy-to-implement protocol. Because stateless protocol is easy, it doesn't have much necessary core code and resources. Another attractive feature of this protocol is that it can be easily switched from one server to another (at the client) or from one client to another (at the server) without much cleaning and tracking. This ability of fast transmission is very suitable for hypertext. (There is a section at the back of this chapter that introduces the definition of hypertext. )
The Internet and everything that comes with it is a very widely distributed network. The standards they support or at least interoperable protocols allow this interoperability to cross academic circles, business circles and even national borders. In other words, the Internet, TCP/IP protocol, HTTP protocol and WWW belong to no one. Schools and companies in different countries can establish clients and servers independently, and they work together on the Web. This implementation method has a great advantage that its expansion space is quite open, if not completely open.
The origin of the World Wide Web
1945 In August, Wan Nivard Bush published an article entitled "As We Think" in Atlantic Monthly. Since then, the idea of electronic linking of document information has been lingering in the minds of computer workers and information scientists.
Writers had anticipated this "connection" long before Bush's article. Isn't the footnote of the article just a "hyperlink" with other works created with paper and pen? Isn't it a further "hyperlink" for writers to quote and learn from other people's works? For example, Lu Xun's and Mao Dun's are also examples of using hypertext in paper environment. This shows that the need to use hypertext has been popular for a long time.
However, it was Bush who linked this idea with electronic technology. Bush foresaw that new technologies developed for war would be widely used and would change our way of thinking. In a word, Bush's basic idea about how to organize and use information has become the WWW and hypertext we see today.
The term hypertext was first put forward by Ted Nelson in 1965. Usually refers to text that is not limited to linear mode. That is to say, some or even all hypertext documents may be linear, but they may also be nonlinear. Hypertext breaks through the limitation of linear mode by linking or quoting other texts. Hypertext is a subset of hypermedia. Hypermedia refers to a kind of media (text, pictures, sound, video, etc. ), linked with other media in a nonlinear way.
Douglas engelbart and Ted Nelson, the inventors of the mouse, first realized the existence of hypertext. Their hypertext implementation was greatly limited by technology and complex design foundation in the 1960s. A two-person project is more imaginative than a feasible project. Nelson named his plan "Xanadu to realize distributed hypertext" in 1967. Xanadu is a project that deals with all copyright and accounting issues. According to him, Xanadu is powerful enough to connect all publications in the world. Although the result was a failure, it laid a solid foundation for the development of hypertext and the World Wide Web.
The emergence of HTML and WWW
1989 In March, CERN, Tim Berners Lee, the European Institute of Particle Physics, put forward a plan to make it easier for scientists to read the articles of their peers. The later goal of this project is to enable scientists to create new documents on the server. To support this project, Tim created a new language to transmit and present hypertext documents. This language is Hypertext Markup Language (HTML). It is a subset of Standard generalized markup language (SGML). SGML has long been proved to be an open language.
The protocol used to manipulate HTML and other WWW documents is called Hypertext Transfer Protocol (HTTP protocol will be introduced in Chapter 2). According to the custom of Internet, almost all protocol names end with TP. The corresponding server is called HTTPD (Hypertext Transfer Protocol Daemon).
HTTP uses the concept of a uniform resource locator (URL). Simply put, a URL is the "address" of a document on the World Wide Web. A URL is used to identify any available data object on the Internet or a host connected to the Internet. The U in URL is often considered to mean "unification", which is actually quoted in many important documents.
There is a basic idea behind the concept of URL, that is, under the condition of providing certain information, you should be able to access any available public data on any machine on the Internet. This specific information consists of the following basic parts of the URL:
The access protocol used.
The machine where the data is located.
The data source port of the requested data
Data path
The standard format of the name URL of the file containing the required data is as follows:
Protocol://Machine Address: Port/Path/File Name
For example, if you want to visit the website of Nanjing University of Science and Technology, its website is:
1July 1992, WWW was widely used in CERN. From then on, WWW was warmly accepted and began to have an impact on the Internet. By June, 1993, 1, there were 50 world-renowned WWW servers and various browser softwares were released. In February of the same year, NCSA (National Supercomputing Application Center) of the University of Illinois at Urbana-Champaign released a new browser software. Since then, WWW has begun to take shape.
Viewing the Development of Browser from Mosaic of NCSA to Netscape
One problem that WWW once had was that it didn't have a reliable general-purpose computer and operating system browser. The appearance of mosaic solved this problem. The NCSA system development team led by Joe Hardin started a project, the goal of which is to build a very useful WWW browser, which can not only handle the WWW described by Tim Berners Lee, but also support other access protocols. This client program, called Mosaic, was released in February 1993.
Many computer experts put forward many new suggestions, which made HTML and WWW develop rapidly. The NCSA team studied the use of MIME (Multipurpose Internet Mail Extension) in detail in order to identify some media formats, especially sounds, pictures, animations and so on. Using MIME types seems to be a natural step, because MIME, a universal Internet mail extension service, has long been regarded as a target that can define and encode most data types. MIME types have new advantages, which are embodied in scalability and proven practicality. Even better, a large number of program codes for operating MIME have already been written and can be used for new programs-WWW client and server programs at any time.
After adding the "IMG" tag to HTML, Mosaic has become a real multimedia browser. Hypertext pages suddenly became much more friendly. Not only the boring academic research information used by scientists and scholars, all kinds of information in today's world can be vividly displayed in the form of multimedia. Since then, the Web has matured, which the Internet has been expecting for a long time.
WWW and network-oriented programming language JAVA
Simply put, JAVA is a new generation programming language developed by SUN Company. The goal of JAVA is to open software in a network environment full of various machines and different operating platforms. This is why no matter what kind of WWW browser, computer and operating system you use, as long as the WWW browser says "Support JAVA", you can see a vivid start page.
Using JAVA programming language, you can add various dynamic effects to your start page, you can put an animation on it, and you can set a neon light on the start page to keep your name spinning on it. If you like, you can also place menus and buttons and scroll bars like ordinary window programs. As long as you use JAVA, there is nothing you can't do.
Why can JAVA do dynamic demonstrations that traditional start pages can't? For nothing else, after adding JAVA support, your start page is no longer just a cold "file", but a living program entity that works with JAVA programs. Because of this, when you use Netscape Navigator or Microsoft Internet Explorer to watch the start pages of various places, the WWW browser you use is not only responsible for displaying the files in HTML format in the correct format, but also for executing the attached JAVA programs on the machine you use.
In fact, for such a JAVA program with its own start page, we have taken a special name called Applet, which can be imagined as a small and lovely program. In addition to developing small applications attached to the start page, JAVA also has the ability to open large applications, and it can be executed anywhere across the limitations of different types of machines and different types of operating platforms.