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

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 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. This text is bold and italic XHTML Elements Must Always Be Closed. This is a paragraph This is another paragraph Empty Elements Must Also Be Closed A break: XHTML Elements Must Be In Lower Case: This is a paragraph XHTML Documents Must Have One Root Element All XHTML elements must be nested within the 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} This heading will be center-aligned 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 Andrew S. Tanenbaum 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.