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The Client-Server Model for the Web

The Client-Server Model for the Web. A Web Client (usually in the form of a web browser) makes an HTTP request to a specific web server. The Web Server receives the request and sends back the requested document (usually in the form of an HTML page).

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The Client-Server Model for the Web

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  1. The Client-Server Model for the Web • A Web Client (usually in the form of a web browser) makes an HTTP request to a specific web server. • The Web Server receives the request and sends back the requested document (usually in the form of an HTML page). • The web client interprets the information returned by the server and displays it appropriately.

  2. Serving Web Pages • Have a computer to act as a ‘server’ to send pages along when requested. • Connect your computer on a network (e.g. the Internet or a local network such as a university) • Install server software that can respond to requests for documents by ‘serving’ them to the requesting computer. • Create and upload the appropriate documents that you wish to make available on the web.

  3. The Server • Have a computer to act as a ‘server’ to send pages along when requested: • A server can be any computer capable of connecting to the internet and running server-software. • The busier the site, the more powerful the computer. However the server can be as simple as your Dell desktop, or as complex as a rack of high-end dedicated computers. • Busy sites (e.g. Google, Microsoft) will have multiple redundant computers to serve their web pages.

  4. Serving web pages: Connecting to the Internet • Most computers today are equipped with network cards that allow them to connect to a workplace network (e.g. school, business). • These networks typically also connect the computer to the internet.

  5. Serving web pages: Server Software • A computer program called a web server listens (constantly) for HTTP requests and responds by sending back HTTP responses. • An example of an http request is: http://www.nytimes.com/index.html • An example of an http response is (usually) the web page document that is sent back to your computer • Several software companies publish web server software • Some of the better known server software programs include: • Apache HTTP Server • Microsoft IIS (Internet Information Services) • Google’s GWS (Google Web Server)

  6. Serving web pages – Creating and uploading information • Good part of what we will do in the rest of this course….

  7. Web clients • Software that is capable of sending out HTTP requests and interpreting HTTP responses. • Recall that HTTP responses are usually (but not always) HTML documents. • The majority of this course will be about creating HTML documents. • The most popular web-clients: • Internet Explorer (published by Microsoft) • Firefox (published by Mozilla Corp.) • Safari (published by Apple) • Chrome (published by Google)

  8. HTML HTML = HyperText Markup Language HyperText text containing navigable links to other texts A Markup Language a method of adding information to the text indicating the logical components of a document and instructions for layout of the text on the page, which can be interpreted by some automatic system You can see the HTML of most web pages by selecting View  Source on your web browser.

  9. HTML: The Language of the Web Web pages are text files written in HTML. HTML is easy to write and even nonprogrammers can learn to use it. HTML allows web page authors to create documents that can be displayed across different operating systems. HTML describes the format of web pages through the use of tags. Web browsers read the HTML file, interpret the HTML tags, and render (display) the web page accordingly Ideally, all browsers should display pages exactly the same. However, different web browsers frequently display pages differently!

  10. Creating Web pages In order to create your own web pages in this course you need: • A text editor (not a web design application like FrontPage or Dreamweaver) (e.g. PSPad, NotePad, WordPad, Textpad) • An web browser for testing the pages(e.g. Firefox, Internet Explorer, Safari, Opera, Chrome – or test with ALL of them!) • A web server to store your files and make them available online (students.depaul.edu)

  11. Basic process for creating web pages Write HTML file • Text file (i.e. do not write in Word) • Assign a file extension (.html or .htm) • View on your local machine (File  Open) Upload to server • All web pages must be inside a directory called public_html (you may have to create this folder) • You may need to set permissions on folders and files (brief tutorial on Unix permissions here) Images: must also be uploaded • All images should be in either .gif or .jpg formats • As with html files, you may need to set permissions on image files

  12. File extensions HTML files must be saved with a .html or .htm extension. • HTML editors like PSPad do this automatically (when you click on File  Save As and choose ‘Save as HTML’) • You must write the extension manually when using a text editor like Notepad, i.e., you must include the .htm extension when saving the file. To make sure your files have the right extension, make the file extensions visible in Windows Explorer (a.k.a. My Documents) by selecting Tools Folder Options  View tab and unchecking the “Hide extensions for known file types” box.

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