Web Pages (CIE IGCSE Computer Science)

• When you type in a URL / click on a link the browser sends the URL to the DNS using HTTP
• The DNS finds the matching IP addresses for the URL and sends the IP address to the web browser
• The web browser sends a request to the web server for web pages
• The web pages are sent from the web server to the browser
• The browser renders HTML to display web pages 
• Any security certificates are exchanged
• SSL/HTTPS is used to secure the data which will encrypt any data that is sent

Structure & Presentation

Websites can be separated into structure and presentation.

HTML is:

• A language used to create the structure/layout of a website
• Written in plain text
• Used in the content layer
• Made up of a set of markup codes
• Used to tell the browser how to display the page 

E.g.

• Where text is placed
• Margins of page
• Line break
• Padding

CSS is:

• A language used to create the presentation / formatting of the page
• Written in plain text
• Used in the presentation layer

• Used by web pages to produce a consistent format between different web pages

E.g.

• Font size
• Font colour
• Background colour

Why are they kept separately?

• The presentation of the page can be changed without needing to alter the structure so regular updates can be made without needing to check the structure
• The formatting document (written in CSS) can be used again for a different website
• If further content and web pages are added to the website, the necessary formatting can be easily applied so this can save time when developing a website
• CSS to standardise formatting so CSS only needs to be created once and be applied to each webpage
• One person can develop the structure and one can develop the presentation so this can save time when developing and updating a website