Introduction to the World Wide Web

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Introduction to the World Wide Web

  1. 1. Introduction to the World Wide Web 1 By: Abdalla Mahmoud . Contents Introduction to the World Wide Web................................................... 1 Contents ........................................................................................... 1 1. Introduction ................................................................................... 3 2. HTTP............................................................................................. 3 2.1. HTTP Request ........................................................................... 4 2.2. HTTP Response ......................................................................... 4 2.3. HTTP Session............................................................................ 4 3. HTML ............................................................................................ 5 4. Web Server.................................................................................... 5 5. Web Browser.................................................................................. 5 6. The Dark Age ................................................................................. 5 7. The Dynamic Age............................................................................ 5 8. Examples....................................................................................... 6 8.1. HTML Skeleton.......................................................................... 6 8.2. HTML Registration Form ............................................................. 6 8.3. HTTP Request ........................................................................... 7 8.4. HTTP Response ......................................................................... 7 8.5. Dynamic Page (JSP) .................................................................. 7 8.5.1. JSP Page ............................................................................ 7 8.5.2. Resulting HTML Document .................................................... 8 1. http://www.abdallamahmoud.com. 1
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  3. 3. 1. Introduction The World Wide Web, or WWW in short, is a system of documents accessed via the internet using standard protocols. The web should not be confused with the internet. The web is described in the terms of protocols and document specifications maintained by the World 2 Wide Web consortium, or W3C in short. Those protocols and documents are clouded on the internet. In other words, the web is a part of the internet. 2. HTTP Hypertext Transfer Protocol, or HTTP in short, is an application level protocol for distributed hypermedia (text, image, video, etc) information systems, developed by the W3C. The main purpose of HTTP is to retrieve inter-linked hypertext documents from the internet. A common example is every day passing time on facebook. You do retrieve different types of media from the facebook website using the HTTP protocol that's familiar to both, the web server hosting the facebook website, and the web browser you use to access facebook website. Some facts about HTTP: • HTTP works in client/server architecture. • The client is the web browser. • The server is the web server. • The client is referred to as the user agent. • The server is referred to the origin server. • HTTP is request/response protocol, i.e. user agent requests, origin server responses, connection is closed. • One consequence of the previous fact is that HTTP is a stateless protocol, i.e. no state is shared between different requests. 2. W3C, founded and headed by Sir Tim Berners-Lee, credited the father of the web. See http://www.w3c.org/. 3
  4. 4. 2.1. HTTP Request An HTTP request is sent by the user agent to a web origin after establishing a connection with it. The purpose of an HTTP request is to retrieve some resource. The request consists of: Request Line: the method of retrieving the resource in addition to the path to this resource. Popular methods are GET and POST. GET Method: parameters can be passed to resources in the URL. POST Method: parameters can be passed to resources also, but the in the body of the request. Request Headers: a set of key-value attributes giving some metadata about the request. 2.2. HTTP Response An HTTP response is sent by the web origin to the user agent before closing the connection with it. The purpose of HTTP response is to reply to the user request with either the resource or some other replies with failure or security insufficiencies. The response consists of: Response Line: Status code (informing reply message) in addition to a textual message. Response Headers: a set of key-value attributes giving some metadata about the response. Resource content: the content of the requested resource. 2.3. HTTP Session Because HTTP is a stateless protocols, stateful applications of user logins and online shop- cards cannot be directly implemented using HTTP. That's because those type of applications needs to remember state among a sequence of requests. To meet this requirement, the concept of HTTP session was introduced. An HTTP session is a set of HTTP requests. The main purpose of a session is to remember state about the client among those requests. This supports all types of applications that needs to make a conversation with the client. An HTTP session is supported by browser- cookies. A browser-cookie is some state that can be stored by the origin server on the user agent and retrieved on later requests. It lets the server remembers some state about a sequence of requests for a specific client. In other words, browser-cookies are variables inside the browser accessed by some origin server. Browser-cookies have expiration-dates that determines the timeout of the HTTP session. 4
  5. 5. 3. HTML Hypertext Markup Language, or HTML in short, is a standard language for representing structural documents of different types of media (text, image, video, etc), developed by the W3C. The main purpose of HTML is to describe the hierarchical structure of a hypermedia page that needs to be rendered using some type of applications called web browsers. Some facts about HTML: • HTML is a representational language, not a programming language. • HTML is rendered using a web browser. • HTML does not do actions. However, scripts of actions can be embedded in some client-side scripting language such as javascript. 4. Web Server A web server is an application that supports hypermedia distribution over the internet. It implements the HTTP protocol and manages different media resources to provide it to users on request. The most popular web server is Apache Web Server. It's open source and can be downloaded from (http://www.apache.org). 5. Web Browser A web browser is an application that used to access and view hypermedia resources managed by some web server using HTTP protocol. It requests resource documents from a web server and render those documents to the viewer. Most popular web browsers are Microsoft Internet Explorer and Mozilla Firefox. 6. The Dark Age Not too long ago, websites was just static HTML pages linked together with no activity with the user. The user is allowed only to view static resources, lazily manually updated by the website administrator. The web was no more just static resources. This feature changed a lot as today websites gradually tended to be web applications. 7. The Dynamic Age Today, most websites are interactive. Users can interact with websites in forms of comments, edits, shares, uploads, etc. For example, the content of the facebook homepage is dynamically changeed every time you visit it as it fetches latest posts by all of your friends. Those types of resources cannot be built in static HTML pages and needs server-side scripting technologies like PHP, ASP, or Servlets and JSP as we will be involved in Java EE. 5
  6. 6. 8. Examples 8.1. HTML Skeleton file: skeleton.html <html> <!-- This is the header section, not displayed on screen --> <head> <title>Page Title Here</title> </head> <!-- This is the body section, displayed on screen --> <body> <h1>Topic</h1> Content </body> </html> 8.2. HTML Registration Form file: registration.html <html> <head> <title>HiQ Training</title> </head> <body> <h1>Student Registration Form</h1> <!-- This is the form section --> <form action="process.jsp" method="POST"> Student Name:<input type="textfield" name="student_name"/> Training Course:<input type="textfield" name="training_course"/> <input type="submit" value="Register"/> </form> </body> 6
  7. 7. </html> 8.3. HTTP Request Internet Explorer <request: http://www.yahoo.com/abc/foo.html> GET /abc/foo.html HTTP/1.1 Host: www.example.com User-Agent: MSIE 6.0 8.4. HTTP Response Web Server <response> HTTP/1.1 200 OK Server: Apache Content-Type: text/html Content-Length: 31837 <html> <!-- Page content goes here --> </html> 8.5. Dynamic Page (JSP) 8.5.1. JSP Page file: foo.jsp <html> <head> <title>First JSP Page</title> </head> <body> <h1> <% int x = 5 ; int y = 7 ; int z = x + y ; out.print(z) ; %> </h1> </body> </html> 7
  8. 8. 8.5.2. Resulting HTML Document browser: <http://www.example.com/foo.jsp> <html> <head> <title>First JSP Page</title> </head> <body> <h1> 12 </h1> </body> </html> 8

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