This is the text document that contains instructions to the browser on how the layout of the webpage should be. It also contains the actual textual content of the webpage. If browser is the builder of the webpage, HTML document is the blue print. When we request for a webpage (for example, type in the URL box www.cnn.com) what gets sent to our computer is an HTML document. Our browser creates webpage on the screen using the instructions in the HTML document.
Browsers are computer programs that interpret HTMl instructions and display the webpage on the user's scrren. The first browser created by graduate students at the University of Illinois Champaign Urbana was called Mosaic. First commercial broswer was Netscape, followed by Internet Explorer, Opera, Safari, Firefox and Chrome. All these are browsers that interpret HTML instructions and display webpages in more or less the same way.
One of the requirements of every communication network is an addressing system for each node. Every individual unit or node in a communication system should have a unique identifier. Consider the global telephone network for instance. Every phone in the whole wide world connected to the telephone network has unique number associated with it. For instance 1 269 387 3592 is assigned only to one phone in the world Ė the one in my office. When someone dials this number from anywhere in the world, only my phone rings. Such unique identifiers are necessary for successful communication. Imagine the confusion, if multiple phones were assigned the same phone number? In a computer network, it is necessary for each computer unit to have a unique identifier or address. On the Internet, each computer is identified by a set of numbers known as the IP address of the computer. (IP stands for Internet Protocol. The addressing conventions were defined in TCP/IP). For example, the IP address of WMUís network computer is 22.214.171.124 which looks almost a like a phone number. When a message is sent to someone with an account at WMU, the network is able to know the computer and its location from its IP address and route the message to WMU. The organization that allocates and manages IP addresses globally is The Internet Corporation for Assigned Names and Numbers (ICANN). It is a non-profit corporation headquartered in California and is responsible for the coordination of the global Internet's systems IP address identifiers and, domain names.
As the number of computers connected to the Internet increased, it became harder to keep track of the numerous IP addresses. When the number of telephones increased, a telephone book was created to record the names of subscribers and their phone numbers. Such a system was developed for IP addresses and is known as the Domain Name System (DNS).Instead of creating a databases like a phonebook that users can look up, DNS assigned easy to remember names to the IP addresses of network computers. For instance, the IP address of CNNís computer is 126.96.36.199. CNN computerís IP address was assigned a domain name www.cnn.com. Users donít have to know the IP address of CNN to access CNN; they just need to remember the domain name which is easier. To access the CNN website, we type in www.cnn.com in our browser. When this information goes to WMUís network computer, it looks up a database of all domain names and IP addresses (much like a telephone book) and routes our request to the IP address corresponding to www.cnn.com. Who maintains the up to date database of all domain names and corresponding IP addresses? A DNS name server is a server that stores this information and responds with answers to queries from other network computers.
Domain names are not randomly assigned to computers but is a hierarchical distributed naming system. A domain name consists of one or more parts orlabels, that are separated by dots. For example, elearning.wmich.edu. The right-most label conveys the top-level domain (TLD). For example the top level domain of elearning.wmich.edu is Ďeduí and indicates that the computer belongs to an educational institution. Some of the other top level domains are: com (commercial computers), gov (government computers), net (telecommunication company computers), org (non-profit organization computers). Please note that this classification according to the type of organization is not strictly followed now. More TLDs have been designated in recent years to meet the demand - biz, info, name, us, cn, and more recently xxx. With the internet becoming more global, ICANN appended an international country label to domain names such as.uk (United Kingdom), au (Australia), in (India), ml (Malaysia), hk (Hong Kong). For example, the domain name of BBC is www.bbc.co.uk.
Although ICANN oversees the administration of IP addresses and domain names, ICANN authorizes and accredits private organizations and entities, known as domain name registrars, to sell domain names to the public on a first-come-first-served basis and to update the domain name registries. Today there are over 500 domain name registrars competing for this business. The biggest registrar today is Godaddy.com. Let us say that we are creating a website for a company called Kalamazoo Taxi Service. You want the website to have a name that will easily be associated with the company and not difficult to remember. So we choose a domain name for the company www.kalamazootaxi.com. Then we visit a domain name registrar like Godaddy.com and check if this name has been bought by someone else and is available for purchase. If it not, we try kalamazootaxi.org, or kalamazootax.net or any other TLD that is available. Let us say that kalamazootaxi.us is available. We can then register that domain name for one or more years and pay Godaddy.com for it.
Let us say, we create the HTML documents containing information about Kalamazoo Taxi Service that we want to publish on the web. This is only the first step to publishing the website. The HTML documents we created will remain only in our PC until we upload these documents into a network computer or server connected to the Internet 24/7. We do use our PCs to connect to the Internet but we need a more stable connection if we want people to be able to access our information any time. Hence, we need a web hosting service that allows us to make our website available to the public 24/7. Web hosts are companies that provide space on their server for their clientsí use. These servers have their own IP addresses. We sign up for an account with a web host who will charge a monthly fee for Ďhostingí our HTML documents (approximately $4-10 per month). We also inform the web host the domain name we have registered for our website. The webhost will then make an entry in the domain registry that our domain name is associated with their IP address and our HTML documents are hosted in their server. Now whenever anyone types in our domain name in their browser, they will be directed to the IP address of our web host and to our account with them.