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DNS – HTTP – DHTML - CSS

ICW Lecture 5 Hasan Qunoo. DNS – HTTP – DHTML - CSS. DNS - Domain Name System. School of Computer Science The University of Birmingham Edgbaston Birmingham B15 2TT United Kingdom. .uk .ac .bham .cs www. DNS - Domain Name System. Everyone has used a DNS.

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DNS – HTTP – DHTML - CSS

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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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