DNS – HTTP – DHTML - CSS ICW Lecture 5 Hasan Qunoo.
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Transcript of DNS – HTTP – DHTML - CSS ICW Lecture 5 Hasan Qunoo.
DNS – HTTP – DHTML - CSS
ICW Lecture 5Hasan Qunoo
DNS - Domain Name System
School of Computer ScienceThe University of BirminghamEdgbastonBirminghamB15 2TTUnited Kingdom
.uk
.ac
.bham
.cswww
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.
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?)
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.
Game Time - Some Tools
• nslookup
• dig
• host
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.
How does HTTP work?
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.
Request methods (Cont.)
• TRACE
• DELETE
• PUT
• OPTIONS
• CONNECT
Tools
• wget
HTML - Hyper Text Markup Language
How can you help the Editor edit the newspaper?
HTML
- Practical Example:- Start an editor.- Simple HTML (Header, Body).- Start adding components (Image,
Headings, Form)- Design a form response page.
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 ClosedA 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...
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.
CSSThe 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*/
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.
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/
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/
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.
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.