Web Basics

In this article, you will learn the basics of the Web and HTML language, to get a better understanding of the Internet architecture, for your ongoing projects.

INTERNET HISTORY

• 1962, Paul Baran, US Air Force: foolproof network project
• 1969: ARPANET: university project
• 1972, Ray Tomlinson: email
• 1975, ARPANET: United States Defense Communications Agency, with NCP protocol
• 1983: Arpanet becomes Internet, with TCP/IP protocol
• 1990: CERN, France: world wide web (www)

You surf the Web thanks to:

• an Internet connection,
• a browser installed on your computer,
• site addresses, or a search tool
• a web server hosting the website, installed in a remote computer

INTERNET / WORLD WIDE WEB

Internet:
Global network, connecting several networks on a planetary scale

WWW:
Huge set of documents stored on computers around the world

• Multimedia hypertext
• Distributed, Multi-platform
• Dynamic, Interactive
• Global
  

INTERNET PROTOCOLS

• TCP/IP:
  Transmission Control Protocol / Internet Protocol
• HTTP:
  HyperText Transfer Protocol
• HTTPS:
  Secure HTTP
• FTP:
  File Transfer Protocol

WHO MANAGES THE WEB?

• The web is not controlled by a single entity,
• It is impossible for a single organization to define the rules of the web
• Two groups have a great influence:
  World Wide Web Consortium or W3 and Browser manufacturers

DEFINITIONS

• Web page:
  Document on the web which may contain text, images, sound and video
  Generally: it is an html file accompanied by otherfiles possibly (images, scripts, etc.)
• Website:
  Set of web pages connected by links, hosted on a web server, and accessible to Internet users
• Web project:
  All the files making up a website, stored in a folder

IP ADDRESS

• Method of addressing computers in the TCP/IP protocol:
  Unique number of a computer in the network
• IP Version 4:
  4 32-bit numbers, ranging from 0 to 255, separated by dots
  Example: 205.237.24.101
• IP Version 6:
  8 numbers of 16 bits each in hexadecimal separated by colons:
  Example: 2001:0db8:0000:85a3:0000:0000:ac1f:8001
• TCP/IP makes it possible to associate names with the IP addresses of the servers thanks to a system called DNS or Domain Name Service, to facilitate use and memorization
  Example: 205.237.24.101 is associated with the name www.cybermachin.qc.ca

URL ADDRESS

Uniform Resource Locator: pointer directed to an element located on the web, such as a web page.
Contains the following information:

• The protocol used: HTTP, FTP, ..
• The name of the server or its IP address, indicating the place where to look for the information: www.cyber.com, 10.1.0.50, …
• The location where the file to access is located in the site, if it is not indicated, a location and a default file is taken
  example: http://www.umontreal.ca/
  http://132.204.5.67

WEB BROWSER

Program that allows you to consult and search for information on the web.
Must be installed on client workstations.
Purpose of browsers:

• interpret and display web pages,
• navigate through web pages,
• Interpret “customer” scripts
• Examples: Microsoft Edge and Mozilla Firefox, Opera, Google Chrome

WEB SERVER

• Program that runs on a remote, powerful computer called a server
• Intended to respond to browser requests
• The browser requests access to a page located on the web server computer, using the HTTP protocol and the server address
• The server sends the requested web page
• The browser then formats the information received from the server.
• The web server is often confused with the computer where the server program is located, which is called Host, because it hosts the website program and files.

WEB APPLICATION

• Application hosted in a web server
• Has a web page interface
• Allows you to create a dynamic website
• Two kinds of technologies coexist
  currently :
  client-side technology
  server side technology

CLIENT-SIDE WEB TECHNOLOGY

• Generally uses languages integrated with browsers, like JavaScript
• The programs (scripts) are interpreted on the client workstation after the page is downloaded
• The processing carried out is light: validations

SERVER-SIDE WEB TECHNOLOGY

• Use server-level languages, such as PHP, ASP, or Java
• Programs (scripts) are executed on the server before the page is downloaded
• The processing carried out is heavy: calculations

DATA ENCRYPTION / COMPRESSION

Data encryption:

• Consists of encoding the information before sending it on the net so that it cannot be intercepted.
• It is decoded upon receipt
• Secure sites use encryption, with the HTTPS protocol
  Example: RSA encryption, …

Data Compression:

• Consists of reducing the size of the information without altering it in order to facilitate its transfer and storage
  Example: zip, jpeg, jar, …

THE DIFFERENT TYPES OF WEBSITES

Are generally classified according to areas of use, in the form of a suffix at the level of website addresses.
The main ones are:

• .com: trade
• .gov: government
• .org: organizations
• .edu: education
• .qc.ca, .fr, …. : depending on the country

INTERNET GLOSSARY

• INTERNET: Network of networks, planetary scale
• World Wide Web or Web: Worldwide web of documents with hypertext links
• TCP/IP: Transmission Control Protocol / Internet Protocol
• IP address: Unique address of a node (such as a computer) on
  Internet
• URL: Uniform Resource Locator, address on the net
• HTTP: Hypertext Transfer Protocol, protocol for transferring
  web pages and data
• HTML language: Hyper Text Meta Language, language of
  web presentation
• Tags: HTML elements, are between < >
• Browser: Client software, sends requests to the web server, such as Edge, Firefox
• Web server: Server software, receives and processes requests from the browser, such as Apache, Tomcat, IIS
• Web page: a hypertext document and hyperlink published on the internet
• Website: set of web pages hosted on a web server
• Website designer: site developer
• Webmaster: Site Administrator

Web Architecture with Proxy and Cache

The proxy-cache plays the same role as your computer’s cache memory: it retains the last data used and when it is requested again, returns it much faster than if it were to be requested for the first time.

Log Files

• Information retained in the log files
• Client IP address
• day + time (hh:mm:ss) of access
• Client browser type (Mozilla, Edge, Opera, Chrome, etc.)
• Resource requested (page or Script)
• Keywords used in search engines
• Execution errors (ex.: 403 Forbidden, 404 file not found, 500 Internal Error, etc.)

The links

To a document in the same folder:
<a href="docB.html">link for document B</a>

To a document in another site:
<a href="http://www.site.com/docB.html">
link for document B in another site
</a>

To an email address:
<a href=“mailto:winckler@irit.fr”>
email from Marco Winckler
< /a>

To a region in another document:
<a href="docB.html#target">
link for the "target" region of document B
</a>

With an image as anchor:
<a href="/">
<img src="logo.gif" alt="home page">
</a>

List with sub elements

<ol type="1">
<li>WEB
<ol type="a">
<li>HTML</li>
<li>CSS</li>
</ol> </li>
<li>Graphiques
<ol type="a">
<li>Images</li>
<li>Drawings</li>
</ol></li>

Tables