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WWW (World Wide Web)

WWW (World Wide Web). Prepared by Ahmed Saad Kareem. Introduction and background.

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WWW (World Wide Web)

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  1. WWW (World Wide Web) Prepared by Ahmed Saad Kareem

  2. Introduction and background • The World Wide Web(WWW) is a repository of information linked together from points all over the world. The WWW has a unique combination of flexibility, portability, and user-friendly features that distinguish it from other services provided by the Internet. The WWW project was initiated by CERN (European Laboratory for Particle Physics) to create a system to handle distributed resources necessary for scientific research [1].

  3. The initial proposal for a web of linked documents came from CERN physicist Tim Berners-Lee in March 1989. The first (text-based) prototype was operational 18 months later. In December 1991, a public demonstration was given at the Hypertext '91 conference in San Antonio, Texas. In 1994, CERN and M.I.T. signed an agreement setting up the World Wide Web Consortium (sometimes abbreviated as W3C), an organization devoted to further developing the Web, standardizing protocols, and encouraging interoperability between sites. Berners-Lee became the director. Since then, several hundred universities and companies have joined the consortium [2].

  4. Architecture • The WWW is a distributed client/server service, in which a client using a browser can access a service using a server. However, the service provided is distributed over many locations called sites, as shown inFigure 1.1.

  5. Client (Browser) A variety of vendors offer commercial browsers that interpret and display a Web document, and all use nearly the same architecture. Each browser usually consists of three parts: • 1- A controller. • 2- Client protocol. • 3- and interpreters.

  6. Server The Web page is stored at the server. Each time a client request arrives, the corresponding document is sent to the client. To improve efficiency, servers normally store requested files in a cache in memory; memory is faster to access than disk. A server can also become more efficient through multithreading or multiprocessing. In this case, a server can answer more than one request at a time[1].

  7. Uniform Resource Locator A client that wants to access a Web page needs the address. To facilitate the access of documents distributed throughout the world, HTTP uses locators. The uniform resource locator (URL) is a standard for specifying any kind of information on the Internet. The URL defines four things: protocol, host computer, port, and path as shown in figure 1.3

  8. Web Documents The documents in the WWW can be grouped into three broad categories: static, dynamic, and active.

  9. 1 Static Document Static documents are fixed-content documents that are created and stored in a server. The client can get only a copy of the document[1]. In other word Web pages are static, that is, are just files sitting on some server waiting to be retrieved. In this context, even a video is a static Web page because it is just a file.

  10. HyperText Markup Language Web pages are currently written in a language called HTML (HyperText Markup Language). HTML allows users to produce Web pages that include text, graphics, and pointers to other Web pages. HTML is a markup language, a language for describing how documents are to be formatted [2].

  11. Dynamic Documents • A dynamic document is created by a Web server whenever a browser requests the document. When a request arrives, the Web server runs an application program or a script that creates the dynamic document. The server returns the output of the program or script as a response to the browser that requested the document.

  12. Active Documents For many applications, we need a program or a script to be run at the client site. These are called active documents for example a program that creates animated graphics on the screen or a program that interacts with the user [1].

  13. Web Service A web service is typically an application programming interface (API) or web API that is accessed via Hyper Text Transfer Protocol (HTTP) and executed on a remote system, hosting the requested service. The W3C defines a "web service" as "a software system designed to support interoperable machine to machine interaction over a network. It has an interface described in a machine-processable format (specifically Web Services Description Language WSDL). Other systems interact with the web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.

  14. The W3C defines a "web service" as "a software system designed to support interoperable machine to machine interaction over a network. It has an interface described in a machine-processable format (specifically Web Services Description Language WSDL). Other systems interact with the web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards

  15. SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks. It relies on Extensible Markup Language (XML) for its message format, and usually relies on other Application Layer protocols, most notably Remote Procedure Call (RPC) and Hypertext Transfer Protocol (HTTP), for message negotiation and transmission. SOAP can form the foundation layer of a web services protocol stack, providing a basic messaging framework upon which web services can be built. This XML based protocol consists of three parts: an envelope, which defines what is in the message and how to process it, a set of encoding rules for expressing instances of application-defined datatypes, and a convention for representing procedure calls and responses.

  16. As an example of how SOAP procedures can be used, a SOAP message could be sent to a web-service-enabled web site, for example, a real-estate price database, with the parameters needed for a search. The site would then return an XML-formatted document with the resulting data, e.g., prices, location, features. Because the data is returned in a standardized machine-parseable format, it could then be integrated directly into a third-party web site or application.

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