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UNIT 13

The World Wide Web

Introduction

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Agenda•The World Wide Web•Search Engines•Video Streaming

Introduction•The World Wide Web:

▫Commonly referred to as WWW or the Web.

▫Is a service on the Internet. It consists of sets of linked documents known as WebPages which can be viewed using a program called a browser.

• Hyperlinks:▫ Are the links on a webpage that contain the web

address of the webpage that will be displayed if the user clicks on the link.

• Web address of a webpage:▫ Also known as URL (Uniform Resource Locator).▫ It consists of a number of separate parts divided by

forward slashes(/).▫ Example : http://www.hw.ac.uk/libWWW/irn/irn.html

http://www.hw.ac.uk/libWWW/irn/irn.html

Protocol prefix:

Hypertext Transfer Protocol

is an agreed communications

standard for WebPages should

be used to transfer the webpages

across the Internet.

Web service:World

Wide Web document (webpage

)

Domain Name:

Indicates the

network domain in which the webpage is stored.

Domain Name Extension:Indicates type of domain.

Country Code: Indicating the location of the computer where the webpage is stored.

The path of the

directory or folder

where the webpage is stored on the server

The name of the

webpage file

Webpage

filename extensio

n

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• IP address (Internet Protocol address ) :▫An IP Address is like a computer's home address.▫It’s a unique 32-bit number identifying each

node on a network e.g. 65.34.254.255

• Domain Name:▫ An identifier used on the Internet in place of the

numerical Internet IP address. ▫ It identifies the host, the type and the country code,

e.g. pnu.edu.sa

•Nodes:▫ A network terminal or point where a computer is

connected to a network.

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Why do we use domain names?• If there were no “domain names”, the user

must enter the (IP Address) of the website !• Some of the more important reasons we use

domain names instead of IP Address include:▫These numbers are not very user friendly and

hard for most people to understand.▫ IP address don't tell you much about what the

service or site is.▫The numbers can be easily mistaken.

• Domain Name System (DNS):▫ A system of associating the name of a device on a

network such as the Internet with its numerical address so that the name can be used by the user and the numerical address can be used by the network system.

• Domain Name Server (DNS Server):▫ A network server computer used for operating and

controlling the domain name system.

• Web server computer:▫The computer storing the web pages.

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What happens when we input a domain name?

• When you type in a web address, a long series of events happen in a very few seconds.

• When a user clicks on a hyperlink on a webpage, or type a web address “e.g. www.pnu.edu.sa” in the browser address bar and press "Enter", the computer begins the following process:

1. The browser program sends a request for pnu.edu.sa to your Internet Service Provider. Each ISP has a Domain Name System Server.

2. The DNS Server look up the IP address of the remote Web Server Computer given in the URL . The DNS Server has a stored table of names and addresses of nodes on the Internet.

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3. The request for the linked webpage is then sent to a router that uses the Internet IP address obtained from the DNS server to route the request (decide on the best Internet path to send the request).

4. The message requesting the webpage is divided up into small sections called packets and each separate data packet is passed from router to router until they all reach the remote web server where they are put back together again.

5. The remote web server sends the requested webpage back to your computer in a similar way using your computer IP address.

6. When the packets arrive to your computer, they are combined and the requested webpage is displayed in the browser.

Router

Router

Router

•Search engine:▫A facility on the Internet that can be used to

search for other websites. ▫ It uses special programs to collect information

about websites on the web and stores the information in a database.

▫Database: a type of applications program used for storing information so that it can be easily searched and sorted.

Search Engines

• To search using a search engine:▫ The user types keywords into a text box called a

search box.▫ The search engine then displays a list of website

links that are relevant to the given keywords.

• Keywords can be used to form search phrases by putting quotation marks around the key words and they can be combined in different ways using logical operators such as OR, AND, NEAR

• Sometimes, symbols such as + or – can be used to represent the operators.

Search Engines

• Special symbols known as wildcards can also be used with keywords. They represent certain characters or combinations of characters. ▫ For example, an asterisk (*) is often used to represent

any combination of characters.▫ A search for ’col*’ would look for any word beginning

with ’col’.

• As well as keywords searches, search engine can be used for field searches. This allows the user to search webpage fields such as the title field of a web page or the web address(URL).

Search Engines

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Example: field searches in Google• Google Advanced Operator: intitle:

Example: manual diagram intitle:toyota will return documents that mention the word "toyota" in their titles, and mention the words "manual" and "diagram" anywhere in the document (title or not).

• Remember: No space between the operator intitle: and the search term.

• The user can store the links to useful websites using bookmark facility in the browser program used to view the WebPages.

•Homepage:▫The web page that is set to be displayed

when the browser program is first started. ▫The user can return to it by clicking the

homepage button in the toolbar at the top of the browser program.

• Because a video signal contains so much data, it is difficult to download it from an Internet server in real time (i.e. so that it can be viewed immediately without any delays or gaps).

• The connection would need to have a huge bandwidth (signal capacity).

• One way of doing this with a normal Internet connection involves using a section of memory as a storage buffer.

Video Streaming

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Video Streaming

• Storage buffer: a storage area for temporarily storing data from a fast source so that it can be fed at a steady rate to a slower system.

• This allows part of the video signal to be downloaded and stored so that the user can begin to view the video before it is completely downloaded.

• Feeding the video signal from the storage buffer to the display makes space in the storage buffer for more of the video to be downloaded.

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Video Streaming

• Therefore, as the user is watching the first part of the video, the next part is being downloaded into the storage buffer.

• The video can therefore be shown to the user at a steady rate.

• This method of downloading video signals using a storage buffer to obtain a steady display is known as Streaming.

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Streaming

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Starter1

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Starter #1

http://www.hw.ac.uk/libWWW/irn/irn.html

Starter 1•Country Code: UK •Document Name: irn.html•Protocol Prefix: http•Domain Name: hw.ac.uk•Directory Path: libWWW/irn•Domain Name Extension: ac•Web Service: www

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Language Work

Language Work: Time clauses

 What is the relationship between each of these pairs of actions ?1: a: You click on a URL. b: Your browser sends it to a DNS server.2: a : The packets are passed from router to router . b : They reach the web server3: a : The packets may travel by different routes . b : They reach the web server .4: a : The individual packets reach the web server . b : They are put back together again .

Language Work: Time clauses

Each pair of actions is linked in time. we can show how actions are linked in time by using time clauses. 1. We can use when to show that one action happens immediately after another action :

When you click on a URL, your browser sends it to a DNS server. 2.We can use once in place of when to emphasise the completion

of the first action. It often occurs with the present perfect.Once the DNS server has found the IP address, it sends the address

back to the browser.

Language Work: Time clauses

3. We can use until to link an action and the limit of that action:The packets are passed from router to router until they reach the web server.

4. We can use before to show that one action precedes another:The packets may travel by different routes before they reach the Web server.

>> If the subjects are the same in both actions, we can use a participle :The packets may travel by different routes before reaching the Web server.

Language Work: Time clauses5.We can use as to link two connected actions happening at

the same time:As the individual packets reach the Web server, they are put

back together again.