Web Pages (Cambridge International IGCSE Computer Science)

Loading a Web Page

Spec point — "4 Explain the purpose and functions of a web browser 5 Describe how web pages are located, retrieved and displayed on a device when a user enters a URL"

Loading a Web Page

How is a web page loaded?

• Web pages are held on web servers (1), known as 'hosting'
• To access a web page on a web server, a web browser is used
• In the browser, a user enters a web page URL (2)
• The browser sends the domain name to a DNS(3)
• The browser connects to the web server and requests to access the page
• HTML(4) is transferred and rendered by the browser, displaying the web page

Web Servers

Spec point — "4 Explain the purpose and functions of a web browser 5 Describe how web pages are located, retrieved and displayed on a device when a user enters a URL"

Web Servers (1)

What is a web server?

• A web server is a remote computer that stores the files needed to display a web page on the Internet
• Web servers are generally available 24/7 and security is managed by the owner of the hardware
• Web servers provide access to multiple users at the same time

Uniform Resource Locator (URL)

Spec point — 5.1.2 · 2 Understand what is meant by a uniform resource locator (URL)

Uniform Resource

Locator (URL) (2)

What is a URL?

• A Uniform Resource Locator (URL) is a unique identifier for a web page, known as the website address
• It is text based to make it easier to remember
• A user enters a URL into a web browser to view a web page
• An example of a URL is:

https://www.savemyexams.com/igcse/computer-science/cie/23/revision-notes/

• A URL can typically be split into three parts:

  • Protocol
  • Domain name
  • Web page/file name

• Using the example about the URL would be split as follows:

Domain Name System (DNS)

Spec point — "4 Explain the purpose and functions of a web browser 5 Describe how web pages are located, retrieved and displayed on a device when a user enters a URL"

Domain Name System (DNS) (3)

What is a DNS?

• The Domain Name System (DNS) can be thought of as the Internet's equivalent to a phone book
• It is essentially a directory of domain names and is used to translate human-readable domain names to the numeric IP addresses that computers use
• When you type a URL into your browser, the DNS translates the domain name into its associated IP address so your computer can connect to the server hosting the website
• Without DNS, we would have to remember the IP address of every site we want to visit

HTML

Spec point — "4 Explain the purpose and functions of a web browser 5 Describe how web pages are located, retrieved and displayed on a device when a user enters a URL"

HTML (4)

What is HTML?

• Hypertext Markup Language (HTML), is the foundational language used to structure and present content on the web
• HTML consists of a series of elements, often referred to as "tags"
• Most tags are opened and closed e.g.<html> and </html>, whereas some tags are only opened e.g.<img> and <link>

Structure

• HTML is used to define the basic structure of a webpage by organising content into sections such as headers, paragraphs, and footers

• The <html> tag is the root element of an HTML page and includes all other HTML elements used to create a page structure

• In this example, HTML is used to create a structure with a header, two sections in the main body, and a footer

• Other examples of HTML being used for structure include:

  • Creating lists to structure information
  • Positioning of text on the screen
  • Embedding media and interactive elements

Present

• HTML is also used to present and display information in a visually meaningful way

• The content layer of a web page is made up of HTML elements such as headings(<h1>, <h2>, etc.), paragraphs(<p>), links(<a>), images(<img>), and more

• This layer is mainly handled by CSS(Cascading Style Sheets)

• In this example, headings(<h1>, <h2>) and text formatting tags (<strong>, <em>) are used to present the content clearly and with emphasis

• Other examples of HTML being used to present information include:

  • Presenting data in a table
  • Displaying images with captions

Worked Example A company sells products over the Internet.

Explain how the information stored on the company’s website is requested by the customer, sent to the customer’s computer and displayed on the screen.

[7]

Answer

Seven from:

Requested

• a web browser is used
• user enters the URL / web address (into the address bar) // clicks a link containing the web address // clicks an element of the webpage
• the URL / web address specifies the protocol
• protocols used are Hyper Text Transfer Protocol (HTTP) / Hyper Text Transfer Protocol Secure (HTTPS)

Sent

• the URL / web address contains the domain name
• the domain name is used to look up the IP address of the company
• the domain name server (DNS) stores an index of domain names and IP addresses
• web browser sends a request to the web server / IP address

Received

• Data for the website is stored on the company’s web server
• webserver sends the data for the website back to the web browser
• web server uses the customer’s IP address to return the data
• the data is transferred into Hyper Text Mark-up Language (HTML)
• HTML is interpreted/rendered by the web browser (to display the website)