Subtitles of the Movie

This next module deals with Internet addresses, or urls as they’re often called. An example of a url is as follows http://www.xyz.com/products/new.htm. This is obviously something you could type into your web browser. The url, this is an example of a url, if you don't know what url stands for, it is Universal Resource Locator or perhaps Uniform Resource Locator. A resource is something you can retrieve from the Internet and this is the locator for getting that. I think it’s important for every budding web publisher to have a really solid understanding of what these url's are and how they work. Let’s analyze each component of this address one by one. Firstly the HTTP part, this is the protocol used to retrieve the document, the protocol, well let’s have some words about that. HTTP in this particular instance is the hypertext transport protocol. There are many other protocols; we'll have a look at some in a moment. Hypertext transport protocol, that is a protocol dedicated to retrieving web pages. So naturally it is the most common protocol used in a web browser. There are many other protocols but they’re not quite so often used in web browsers, now protocol itself is a communications language used by two computers to communicate with each other. So in this particular instance, HTTP, the hypertext transport protocol is a communications language used by 2 computers to share web pages and images and so forth like that. Other protocols include FTP, which is the File Transfer Protocol SMTP, Simple Mail Transport Protocol, POP, the Post Office Protocol, NNTP the Network News Transport Protocol and many others. those are just some examples. So when you type HTTP at the beginning of your url, what you’re actually saying is, I want this resource whatever it is, probably going to be a web page to be retrieved using the HTTP protocol. If your browser supports other protocols like FTP, then you could type that instead assuming that the server that you’re connecting to also supports that protocol. Next we’ll just have a look at the dot com part of the www.xyz.com, that's the top level domain We'll talk more about those later, top level domains we've got .com, .org, .net, .gov, .mil and .adu are the six current top level domains although they’re introducing more in the very near future. But we won't talk about those just at the moment, we have got a whole chapter on domain names so we’ll talk about those then. The xyz.com part, that's the domain name of the organization, the domain name, sorry, the organization will have registered somewhere a domain name, we'll talk about where you register them later, so the domain name is… Well, it's essentially a name given to the network of computers that that particular organization owns. An example would be Microsoft.com or Volvo.com obviously you know what these are. Let’s move on. It is important to note that any computer that is part of that organization’s network, if that computer has a name that name will end in xyz.com in this particular case. So you could have a computer on that network and you could call that computer Fred, so that computers name the full computers name would be Fred.xyz.com. So it follows then that www.xyz.com is the name of the machine It's the www machine in the xyz.com network. So why is it called www? Well, just by convention. What most organizations do, not all but most is that they take the computer that is going to be dedicated to serving web pages to the rest of the world, the computer where they put all their web pages that they want the rest of the world to see and they name that machine the www machine. Why? Because it's easy to remember, because most of the people in the world think of www when they think of browsing the web. So it’s just a convention, doesn't have to be called www, it could be called Fred. When a company is advertising their web page, they could just say go to http://Fred.xyz.com but that's probably going to be harder to remember then www.xyz.com, so they stick with www. Finally the rest of that url, /product/new.htm, well that refers to the document that you’re trying to retrieve so we are trying to retrieve the document called new.htm, which in fact is probably a web page in the products directory of the www machine’s hard disk. If you don't specify the documents that you want, if you just said htttp://www.xyz.com and you didn't specify anything after that, then it would be up to the software running on the www machine to decide which web page is retrieved for you. So it would typically give you the table of contents page or the main index page of the organization, the home page if you like. Now that is a good run through of each of the elements of a url. So what does it mean when you type that into your browser. When you type that into your browser, what you’re essentially saying to your browser, you’re issuing instructions to your browser and the instruction is as follows, contact the machine called www.xyz.com using the HTTP protocol and ask for the file called new.htm in the products directory, so obviously your browser has to do that. Now there is an implicit instruction there as well that is when you receive that file display it on the screen, that kind of goes without saying. Interesting things to note: in order for all of this to take place, there must be a program running on the remote computer and the remote computer here I’m talking about is the www.xyz.com computer that is capable of speaking the HTTP language. Now they call these programs web servers, web server software, web server programs. In other words, there must exist web server software running on www.xyz.com machine, if there is not that software running there you simply cannot communicate with that computer using the HTTP protocol. Now interestingly the remote computer itself the computer is often referred to as a web server. So there is a bit of an overload of terms here, the term web server can refer to the hardware in other words, the computer itself, say that computer over there is a web server or it can refer to the software running on that computer that speaks the HTTP language, just be careful when you’re using the term web server as to what you’re referring. Now finally the most popular web server software around at the moment is called Apache. Apache runs on many operating system platforms, Unix, Windows and others. It's free by the way; you can download it from www.apache.org. In the next module, we'll discuss what happens technically when you actually issue this particular instruction to your browser.