Introduction

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Introduction...

People access websites using a software called a web browser (such as Firefox, Chrome or Safari). When people ask their browser for a webpage, the request is sent across the Internet to a web server which hosts the websites. Web servers are special computers that are constantly connected to the Internet and are optimized to send webpages out to people who request them.

Every time a user types a domain name (such as ulb.be) into their browser window, it triggers the DNS lookup. The Domain Name System (DNS) servers find the IP address of the domain and send it back to the user computer. The user can thus access the correct IP address. To communicate with web servers, communication protocol is the HTTP. HTTP is indeed designed to enable communication between clients and web servers. It works as a request-response protocol between a client and server. There are two main common HTTP methods:

  • GET is used to request data from a specified source
  • POST is used to send data to a server to create/update a resource (cf. a form)

GET is less secure compared to POST because data sent is part of the URL.

Screenshot - Valentin's videos.png

The worldwide web uses three technologies to do this:

  1. The HTTP for hypertext transfer protocol: it is the foundation of data communication for the web
  2. The HTML: the main mark up language for creating webpages and information that can be displayed on a web browser
  3. The URL which is used to reference a web page

File Transfer Protocol (FTP) is an application layer protocol which moves files between local and remote file systems. It runs on the top of TCP, like HTTP.

A computer server is a computer device (hardware and software) that provides services to one or more clients. There are other Internet services:

  • Mail server (SMTP)
  • File server (FTP)
  • DNS server (DNS)
  • Identity server (LDAP)
  • Web server (HTTP)
  • VoIP FaceTime (SIP)

When we talk about webpages, we mainly talk about 3 technologies: HTML, CSS and JavaScript. Content Management System (CMS) produces HTML and CSS. HTML is the main skeleton for every website, it is the structure. It contains all the content organized into a logical structure (headline, paragraphs, images, etc.). CSS is used for making your website look much better, it is more about style (background colour, front size, etc.). Then, JavaScript is used for the interactivity of the website, it is the behaviour (what happen if you click on this picture, etc.).

Where to go?

Main page Exercises - Next Session HTML