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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)                      9  TCP/IP World Wide Web and Hypertext Overview and Concepts

World Wide Web and Hypertext Overview and History 1 2 3 World Wide Web Media and the Hypertext Markup Language (HTML)

Major Functional Components of the Web

We know that equating the Web to the entire Internet is not a precise use of terms, but it shows how important the Web is and how closely it is tied to the Internet. Still, while the Internet and TCP/IP are obviously important parts of the Web's success, they are generic in nature. When it comes to defining the World Wide Web system itself more specifically, three particular components are usually considered most essential:

• HyperText Markup Language (HTML): A text language used to define hypertext documents. The idea behind HTML was to add simple constructs, called tags, to regular text documents, to enable the linking of one document to another, as well as to allow special data formatting and the combining of different types of media. HTML has become the standard language for implementing information in hypertext, and has spawned the creation of numerous other related languages.
  
  
• Hypertext Transfer Protocol (HTTP): The TCP/IP application-layer protocol that implements the World Wide Web, by enabling the transfer of hypertext documents and other files between a client and server. HTTP began as a very crude protocol for transferring HTML documents between computers, and has evolved to a full-featured and sophisticated messaging protocol. It supports transfers of many different kinds of documents, streaming of multiple files on a connection, and various advanced features including caching, proxying and authentication.
  
  
• Uniform Resource Identifiers (URIs): A method of defining labels that identify resources on an internet so that they can be easily found and referenced. URIs were originally developed to provide a means by which the users of the Web could locate hypertext documents so they could be retrieved. URIs are actually not specific to the Web, though they are most often associated with the Web and HTTP.

All three of these were created and developed at around the same time, and taken together represent the key technologies that define the World Wide Web. The next two topics in this section describe HTML and the use of URIs in the context of the World Wide Web. HTTP is really the heart of the Web and is covered extensively in its own section later in this Guide.

World Wide Web and Hypertext Overview and History 1 2 3 World Wide Web Media and the Hypertext Markup Language (HTML)