Class 2: HTML, Client/Server Model, and The Internet

Class notes for 11/21/2013.

Transcript

1. HTML, Client/Server, and The Internet Class Two: November 21, 2013
2. The First Website
3. Sad Al Gore is Sad
4. THX TIM, I LUV MAH INTERNET!
5. HTML: Hyper Text Markup Language HTML is a “markup language” that tells how a webpage should be formatted. A web browser is capable of requesting a page from a web server and interpreting the results. Tim Berners-Lee is the inventor of the Web. In 1989, Tim was working in a computing services section of CERN when he came up with the concept; at the time he had no idea that it would be implemented on such an enormous scale. Particle physics research often involves collaboration among institutes from all over the world. Tim had the idea of enabling researchers from remote sites in the world to organize and pool together information. But far from simply making available a large number of research documents as files that could be downloaded to individual computers, he suggested that you could actually link the text in the files themselves A chapter on the history of HTML, if interested.
6. Client/Server Model A server is a computer system that selectively shares its resources. A client is a computer or computer program that initiates contact with a server in order to make use of a resource. Clients and servers exchange messages in a request- response messaging pattern: The client sends a request, and the server returns a response. To communicate, the computers must have a common language, and they must follow rules so that both the client and the server know what to expect.
7. Web Browsers The purpose of a web browser is to read HTML documents and compose them into visible or audible web pages. The browser does not display the HTML tags, but uses the tags to interpret the content of the page.
8. Hosts, IP Addresses, and DNS Take http://www.saxifrageschool.org/index.html. First, your browser has to establish a connection to the host www.saxifrageschool.org. This host corresponds with a numeric value known as an IP (Internet Protocol) address. What’s my IP? The “phone book” that translates hosts to IP addresses is called DNS (Domain Name System).
9. HTTP (Hyper-Text Transfer Protocol) HTTP functions as a request-response protocol in the client- server computing model. A web browser, for example, may be the client and an application running on a computer hosting a web site may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, returns a response message to the client. The response contains completion status information about the request and may also contain requested content in its message body.
10. Packets Packets are parts of a file that range between 1,000 and 1,500 bytes. Packets have headers and footers that tell computers what's in the packet and how the information fits with other packets to create an entire file. When the packets get to you, your device arranges them according to the rules of the protocols. It's kind of like putting together a jigsaw puzzle. The end result is that you see this article.
11. Packets Each packet travels back up the network and down to your computer. Packets don't necessarily all take the same path -- they'll generally travel the path of least resistance. That's an important feature. Because packets can travel multiple paths to get to their destination, it's possible for information to route around congested areas on the Internet. In fact, as long as some connections remain, entire sections of the Internet could go down and information could still travel from one section to another -- though it might take longer than normal.
12. Internet Backbone
13. Demo from My Site My web hosting company is currently DreamHost. My URL (Uniform Resource Locator) is www.logicnest.com Let’s look at an example to tie these ideas together.
14. Non-Standard HTML In the early years of the World Wide Web, the standards which today are used in most web browsers and web pages were mostly non-existent. Imagine a world in which <p></p> is interpreted differently by each browser. Oh no! <blink>This is a bad idea.</blink>
15. The World’s Worst Website Ever! Also, HTML hell.