Introduction to Web Development

The Internet and the Web

The internet and the Web are two distinct things, although the two are often used synonymously. The internet is a massive network of networks. It is the physical infrastructure that connects users together. This physical infrastructure includes switches, routers and satellite links (to name a few). The internet is a global network that allows any computer on the network to communicate with any other computer. The Web is a way of accessing information that is stored on devices connected to the internet. It is a set of protocols and services that make sharing information easy. For the case of HTML documents, the protocol used is HTTP. This protocol facilitates the requesting of resources stored on devices connected to the internet. HTML supports the linking of documents. One HTML document will link to another and in turn will point to another. This linking structure gives rise to the name "the Web". The structure of the Web can be likened to a spiders web, a huge collection of documents connected together by strands of silk.

While most of the general public primarily use the internet to browse web pages, there is much more to the internet than just the Web. The internet is used to transfer research data, to synchronise clocks, to stream video and audio, and more. In general the internet can be used for any task which involves the communication of data from one computer to another.

The architecture of the internet

As mentioned before, the internet is the physical infrastructure that facilitates the transfer of data from one computer to another. Although this module does not intend to teach networking, it is essential to have a fundamental understanding to be able to understand how the Web works. The internet is made up of links, switching and routing infrastructure and computers. The links that make up the internet can take many different forms. Some are copper - using electric signals, some are glass (fibre optic) - using light, and some use electromagnetic radiation to transfer data. Although the medium used by these links is different, their purpose is the same: to transport data from one endpoint to the next. The endpoints of these links are either computers or switching and routing infrastructures. Let us consider the purpose of switching and routing infrastructure. The transmission of data on the internet can be likened to sending a letter through the post. A message gets written and gets an address written on the envelope. The letter is then posted and enters the mail system. The messages is sent through a series of post offices, and at each step the letter gets closer to its destination. At the post office the letter gets sorted and forwarded to the next post office until eventually the post office can deliver it to the door of the recipient. In this analogy the letter is the packet of data: the roads that carry the letters between post offices are the links, the post offices are switches and routers and the sender and receiver of the letter are computers.

The architecture of the Web

The Web is the interconnected collection of documents available on the internet. The Web is made up of individual web pages which 'cluster' together to form web sites. Between pages there are links which allow users to navigate the web of documents. The type of the documents linked to in the web can be anything. Usually these documents are HTML documents which contain links to other documents. The Web has evolved since its conception, but the principles are mostly the same.

The web uses a client-server model. That is, there are computers on the internet whose sole task is to serve webpages that are requested by other computers. A computer on the internet that serves webpages is called a web server. A machine that requests pages from a web server is called a client, more specifically we refer to the specific application that is running on the client that makes the request for webpages as a web browser. The responsibility of a web browser is to request webpages from the server and to display them for the user. There are also automated clients that request webpages that will not be displayed to users - these are called bots. The purpose of such bots is to perform data mining or indexing.

A history of HTML

As mentioned in the previous section the internet is distinct from the web. Before HTML and the web there was the internet. The internet was originally designed as a defence network to send information between military command centers. The use of the internet was restricted to government agencies and research institutes. In 1969 the internet was open up and universities and other authorised used were able to connect devices together. In 1990 Tim Berners-Lee, while working at CERN, proposed a document that described a way of connecting documents together. This document outlined the foundation of the World wide Web. Along with the proposal Tim -Berners-Lee defined a language for describing these documents and outlined how they should be managed collaboratively. This language was HyperText Markup Language (HTML). When the World Wide Web was proposed the philosophy of the web was very different to the web today. The intent was to have a web of documents that would be edited by anyone, this could be compared to Wiki's. In some ways Wiki's are the closest thing we have that captures the original philosophy of the web, however, the means by which Wiki's achieve this ideal is very different. The developement of HTML is an evolutionary one, mostly different by developers. The evolution is then standardised by a range of different bodies. HTML was not the first of its kind, before HTML there existed a description language called Standard Generalised Markup Language (SGML) which used a similar format to HTML. The first official standard for HTML was HTML version 2, which was written by the Internet Engineering Task Force (IETF). The IETF was later superceeded by the World Wide Web Consortium (W3C). The W3C continued to standardise features into the HTML language which developers had been using. This was until the W3C shifted their focus on to Extensible HyperText Markup Language (XHTML), which was a step towards converting HTML into Extensible Markup Language. This transistion however was not smooth with many of the popular browsers of the time refusing to implement XHTML. While the W3c toiled to encourage the adoption of XHTML a separate group was setup called the Web HyperText Application Technology Working Group (WHATWG). The internal structure of these two groups was slightly different and these differences allowed the WHATWG to move quickly to standardise new features which was essential in the rapidly developing World Wide Web. In 2009 the W3C publicly dropped he development of XHTML and joined forces with the WHATWG to develop HTML5.