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DNS, HTTP, DHTML, CSS: Exploring Web Technologies

Learn about the Domain Name System (DNS), Hypertext Transfer Protocol (HTTP), Dynamic HTML (DHTML), and Cascading Style Sheets (CSS) in this informative lecture. Understand the role of DNS in translating domain names into IP addresses, the workings of HTTP for data transfer, and the power of DHTML and CSS in web design. Explore practical examples, tools, and resources for mastering these web technologies.

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DNS, HTTP, DHTML, CSS: Exploring Web Technologies

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  1. ICW Lecture 5 Hasan Qunoo DNS – HTTP – DHTML - CSS

  2. DNS - Domain Name System School of Computer Science The University of Birmingham Edgbaston Birmingham B15 2TT United Kingdom .uk .ac .bham .cs www

  3. DNS - Domain Name System • Everyone has used a DNS. • The DNS system forms one of the largest and most active distributed databases on the planet. • a hierarchical, domain-based naming scheme and a distributed database system for implementing this naming scheme. • Every machine on the Internet has its own IP address. Some static and some dynamic. • An IP address is all that you need to talk to a server. • Domain names are strictly a human convenience.

  4. DNS - Domain Name System • The DNS system is a database • It translates symbolic hostnames into the numerical IP addresses. • Example: • www.cs.bham.ac.uk   147.188.192.42 • www.bham.ac.uk 147.188.125.57 • www.google.com  74.125.43.105 • A single URL can be resolved into more than one IP. (Why?)

  5. DNS- How does it work? • When a request comes in: • DNS can answer the request with an IP address because it already knows the IP address for the domain. • DNS can contact another name server and try to find the IP address for the name requested. It may have to do this multiple times. • DNS can say, "I don't know the IP address for the domain you requested, but here's the IP address for a name server that knows more than I do." • DNS can return an error message because the requested domain name is invalid or does not exist.

  6. DNS- Applet • Applet

  7. Game Time - Some Tools • nslookup • dig • host

  8. HTTP- Hypertext Transfer Protocol • HTTP is an application-level protocol  • HTTP is used to transfer data on the Web. • HTTP led to the establishment of the World Wide Web in 1990 by English physicist Tim Berners-Lee.

  9. How does HTTP work?

  10. Request methods • GET • Requests a file from the server.  • POST • Submits data to be processed (e.g., from an HTML form) to the identified resource. • HEAD • Same as GET without the body.

  11. Request methods (Cont.) • TRACE • DELETE • PUT • OPTIONS • CONNECT

  12. Tools • wget

  13. HTML - Hyper Text Markup Language How can you help the Editor edit the newspaper?

  14. HTML • Practical Example: • Start an editor. • Simple HTML (Header, Body). • Start adding components (Image, Headings, Form) • Design a form response page.

  15. XHTML/HTML • XHTML is a stricter and cleaner version of HTML: • XHTML Elements Must Be Properly Nested. • <b><i>This text is bold and italic</i></b> • XHTML Elements Must Always Be Closed. • <p>This is a paragraph</p><p>This is another paragraph</p> • Empty Elements Must Also Be Closed • A break: <br /> • XHTML Elements Must Be In Lower Case: • <body><p>This is a paragraph</p></body> • XHTML Documents Must Have One Root ElementAll XHTML elements must be nested within the <html> root element. • The List Goes On...

  16. CSS • HTML was never intended to contain tags for formatting a document. • Imagin you have to edit every HTML page every time you want to change the style. NIGHTMARE! • Do not worry CSS to the rescue.

  17. CSS • The CSS syntax: • selector {property:value} • Example: • p {font-family:"sans serif"} • You can also group selectors: • h1,h2,h3,h4,h5,h6 { color:green} • You can select by Class: • h1.center{text-align:center} • <h1 class="center"> • This heading will be center-aligned • </h1> • Comments: /*This is a comment*/

  18. Example • Practical Example: • Start an editor. • Create a css file. • Add simple modifications to the style. • Modify the HTML file. • Style the HTML form from previous example. • Display the file on the browser.

  19. Resources • HTML, XHTML and CSS tutorials: • http://www.w3schools.com • Web Standards • http://www.w3.org/ • Validations • http://validator.w3.org/ • Free CSS Templates: • http://www.csszengarden.com/

  20. Resources • List of all the css properties: • http://htmlhelp.com/reference/css/all-properties.html • Domain Name Service DNS • Computer Networks, Fourth Edition By Andrew S. Tanenbaum Chapter 7 • HTTP Protocol RFCs • http://www.w3.org/Protocols/ • Free CSS Templates: • http://www.csszengarden.com/

  21. Exercise • Using nslookup, host and dig Commands, find the IP addresses for the following URLs: • www.bham.ac.uk • www.google.co.uk • www.cs.bham.ac.uk • www.w3school.com • The first 5 students to send me the correct commands and their output will get a prize each.

  22. Conclusion • There are many types of technologies which are used to support the world wide web and more are being developed all the time.  • There are many resources to learn more about each of these Technologies. • Designing web pages is fun.

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