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  • 1. INFT11/71-132 Web Applications Web Concepts Dr Michael Rees School of Information Technology mrees@bond.edu.au
  • 2. Internet v Web • Internet is the basic infrastructure • The Web provides a linked, information structure – web pages • Uses Hypertext Transfer Protocol (HTTP) to transfer web pages • Web pages use a document structure called Hypertext Markup Language (HTML) • HTML contains tags that define the content and layout of the web pages © 2009 Michael Rees Web Applications 2
  • 3. Web Software Technology • Web server: – Software that serves web pages and related files (entities) – Supports HTTP • Web client (browser): – Internet host machine running client application – Initiates HTTP requests to designated web server to retrieve web pages and other files (entities) – Displays (or saves or executes) retrieved entities © 2009 Michael Rees Web Applications 3
  • 4. Retrieving a Web Page 1. Browser acquires a URL 2. Browser uses DNS to determine the IP address of the web server 3. Using HTTP protocol, browser sends a request to the web server at that IP address for the named web page 4. Web server received request via HTTP, locates the file requested and transmits HTML content back to the browser via HTTP 5. The browser interprets the HTML and displays the page on the screen This is the request-response cycle © 2009 Michael Rees Web Applications 4
  • 5. HTTP Request–Response cycle 1. Open TCP 2. Request + [Entity] Connection Web Web Browser Server (Client) 5. Interpret & 3. Check Request 4. Response + [Entity] Display • syntax 6. Close TCP • existence Connection • authentication © 2009 Michael Rees Web Applications 5
  • 6. Uniform Resource Identifier - URI • Two types of URI: – Uniform Resource Name - URN • Used to identify resources with unique names, such as books (which have unique ISBN’s) • Scheme is urn • Example: urn:foo:a123,456 – Uniform Resource Locator - URL • Specifies location at which a resource can be found • http scheme, others are https, ftp, mailto, and file • Example: http://www.bond.edu.au/bondit/index.htm © 2009 Michael Rees Web Applications 6
  • 7. HTTP • Implemented over a TCP connection • 80 is the standard port number used • Request: – Command line – Additional header lines – Blank line – Optional content • Response: – Status code More details on HTTP – Additional header lines – Blank line – Optional content © 2009 Michael Rees Web Applications 7
  • 8. HTTP Example • To acquire: • Response http://www.somehost.com/path/file.html HTTP/1.0 200 OK Date: Fri, 31 Dec 1999 23:59:59 GMT • Request Content-Type: text/html Content-Length: 1354 GET /path/file.html HTTP/1.0 From: someuser@tutorialspoint.com <html> User-Agent: HTTPTool/1.0 <body> [blank line here] <h1>Happy New Millennium!</h1> (more file contents) . . . </body> </html> © 2009 Michael Rees Web Applications 8
  • 9. Multipurpose Internet Mail Extensions • Abbreviated to MIME • Convention for specifying content type of a message – In HTTP, typically used to specify content type of the body of the response • MIME content type syntax: – top-level type / subtype • Examples: text/html, image/jpeg © 2009 Michael Rees Web Applications 9
  • 10. Secure Servers • HTTP messages typically travel over a public network • Private information (such as credit card numbers) should be encrypted to prevent eavesdropping • https URL scheme tells browser to use encryption • Common encryption standards: – Secure Socket Layer (SSL) – Transport Layer Security (TLS) © 2009 Michael Rees Web Applications 10
  • 11. Secure Servers I’d like to talk securely to you (over port 443) HTTP Here’s my certificate and encryption data HTTP Requests Requests Here’s an encrypted HTTP request TLS/ Here’s an encrypted HTTP response TLS/ Web Browser SSL SSL Server Here’s an encrypted HTTP request HTTP HTTP Responses Here’s an encrypted HTTP response Responses © 2009 Michael Rees Web Applications 11
  • 12. Resources • Read Sections 1.1 through 1.8 of textbook © 2009 Michael Rees Web Applications 12