What is the World Wide Web Architecture

3.1 Concepts of the World Wide Web


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There are three basic concepts or principles that characterize the World Wide Web: Hypermedia, the Client-server architecture and the so-called Uniform Resource Locators. They are the subject of this chapter.

3.1.1 Hypermedia

 

Hypertext

The starting concept of the WWW applies Hypertext. This is to be understood as a type of text that removes the linearity of text. This is achieved through the introduction of Left reached.

A link (English for reference) is a word or, in general, a piece of text which, when clicked, leads to another section of text.

This tool is used to lead to more detailed explanations, further explanations or generally context-dependent passages.

Web browsers usually display links in blue and are also underlined.

multimedia

In the early days of computers, writing was the medium of choice either on the screen or in printed form on paper. Graphics later came into play, which, by adding auditory abilities to computers, rounds off a media package that is known in its entirety as multimedia designated.

Hypermedia

Under Hypermedia one understands the amalgamation of Hypertext and multimedia to a medium which, in its way of dealing with text and multimedia elements, represents a novel concept for the presentation of information.

3.1.2 Client-server architecture

As with all Internet services, the client-server architecture is also used in the World Wide Web. By that one understands a

,, Cooperative information processing, in which the tasks are divided between programs on connected computers. server (= Service providers) offer services via the network, Clients (= Customers) request this if necessary '' ([48], page 64).

Another distinction is made between a user-oriented part (= client) and a part (= server) of an information system that is shared by all users (cf. [48], page 1031). The task of the servers in the World Wide Web is to keep WWW pages ready for retrieval. In addition to the storage space for the documents, an Internet connection with a corresponding domain name (e.g.) is of course required, by specifying which the pages can be called up. WWW servers are mainly operated by Internet providers and research organizations (including universities); the former provide companies and private individuals with storage space for their online documents for a fee (cf. [174], page 2 f).

To call up the information offered in this way, the user needs a client program on the World Wide Web Browser mentioned (see chapter 3.2). Its job is on the one hand to take care of the connection to the server and to request the data from there. On the other hand, the information received must be processed optically, since only a sequence of characters is transmitted over the Internet connection (more on this in Chapter 3.3).

3.1.3 Uniform Resource Locators

 

The third fundamental concept of the World Wide Web is that of Uniform Resource Locators, usually short as Urls designated. This is understood to be name information with the help of which every document on the Internet can be clearly identified.

The Beginner's Guide to URLs on the World Wide Web writes about this:

,, Think of it as a networked extension of the standard filename concept: not only can you point to a file in a directory, but that file and that directory can exist on any machine on the network, can be served via any of several different methods, and might not even be something as simple as a file '' ([99]).

The general form of a Uniform Resource Locator is

protocol:

This structure can roughly be compared to a postal address in the following form:

Registered mail:

The type of transport corresponds to the protocol, the address to the domain name of the host, the department to the directory path (or the sequence of folders) and the name of the recipient to the respective document.

The protocol in the WWW is usually HTTP. This abbreviation stands for Hypertext Transfer Protocol, which is based on TCP / IP and regulates the transfer of data between the WWW server and client. Usually comes a simple one Get-Principle of application: The client sends a so-called Request. The server reacts by transmitting the requested data (Response) and terminates the connection, which therefore only lasts very briefly (cf. [137], page 178 f).

Sometimes it is necessary to access another Internet service from the WWW browser, which is based on a different protocol. This is also possible without any problems, even if there is a slight deviation from the general form described above. Table 3.1 shows an overview of the most important protocols (cf. [174], page 318 ff; [48], page 392; [99]).

 
Table 3.1: Protocols for URLs

Unfortunately, despite all its ingenuity, the URL concept also has a decisive disadvantage: The documents are only available once in the entire Hyperspace. Frequently requested pages can easily overload the relevant server, which means an extremely long waiting time for the user.

The system of URNs, the Uniform Resource Names that has been tinkered with since 1991. The document is saved under a unique name in several places around the world; a central list provides information about the hosting hosts. If the document is called up by the client, it can be obtained directly from the nearest server or the server that is currently best accessible (cf. [174], page 5 f).

URLs and URNs are combined as URIs - Uniform Resource Identifiers - designated. A URN is therefore `` Any URI which is not a URL '' ([120]).

 
Figure 3.1:Uniform Resource Identifiers



Next:3.2 browserUp:3 WWW Previous:3 WWWThomas Neurauter
Sun May 3 18:05:51 CEST 1998