1. Creating Web Documents: How the Web works Client / Server Protocols Access methods Homework: Complete experiment & report on Discussion Forum

2. How the web works Client/server: server, holding information receives requests from client (you/your browser). Typical request is for a file Protocols = rules to be followed by different computer programs. Many protocols are involved. –Transmission Control Protocol/Internet Protocol controls transmission of packets (files divided into smaller pieces) and routing to the address. Uniform Resource Locator indicates which protocol (e.g., http://, ftp, mailto) and which server address (domain name possibly followed by directories & file names –Route of packets can vary, so transmission needs to be reassembled at each end.

3. tracert Route from one point to another can be many steps and can vary. This redundancy is basic characteristic of the Web On Windows machine, click on Start/Run/ to get command prompt: type in command if not present After > type in tracert URL >tracert www.nytimes.com

4. How the web works, cont. Hypertext Transfer Protocol –Client opens the connection, at URL and at port –Client makes a request –Server sends response –Connection closed An HTML file with 2 images requires 3 connections. No information kept between connections = stateless system

5. cache More complex Files are stored in what is called the cache. –Maybe local cache and network cache. Browser 'looks around' to see if there is already a copy of the file requested. May send a message to check on time to see if this file has been updated. Generally works BUT sometimes, you may need to exit and re-invoke browser or even clear out cache to get latest version.

6. Server side programming Programs (scripts) run on server to handle databases, files, other computations. Use common gateway interface (cgi). –You may read about cgi/perl programs New[er] middleware systems: asp, php, cold fusion –Topic of Creating Databases for Web Applications course. When server gets request for a file of type pl, php, asp, cf, it executes the file instead of returning it as is to the browser. These programs create HTML file dynamically, possibly using information stored on server.

7. Connections Dial-up phone service. A modem changes the computer (digital signal) to electronic and a modem at other end changes electronic back to digital. Faster connections are referred to as broadband DSL (digital subscriber line) a technology that exploits unused frequencies on copper telephone lines to transmit traffic typically at multi-megabit speeds. DSL can allow voice and high-speed data to be sent simultaneously over the same line. Because the service is 'always available,' end-users don't need to dial in or wait for call set-up. Cable modem: uses the cable line.

8. Browser Interprets the HTML document Displays the text Tags set up action for what is between the tags Image files and other media are displayed by browser itself or by call to a helper/plugin program The a tag (and tags for forms) set up new requests to servers.

9. Other browsers Personal Digital Assistants (PDAs) and cell phones have special and distinct browsers. Wireless Application Protocol (WAP) enabled phones are an example. These browsers work with slower connections, less storage space. Also refer to WAP enabled sites: sites specialized for use by WAP phones. Use Wireless Markup Language and Wmlscript. –One of several topics in Creating User Interfaces. IF YOU HAVE such a phone, use it for the experiment!

10. Uploading projects to our web site File management –Multiple files for ‘web page’ –For now, keep each project in one directory –Make name of main HTML file (probably only have one) index.html –Keep names simple: lower case, no spaces Critical if server operating system not the one you are using for development Ws-ftp (file transfer protocol)

11. The Link to (external) web site href=http://..... Link to html file on same server, same folder href="filename.html" Link to html file on same server, in parent folder href="../filename.html" Link to place in same file href="#place"

12. Assignment Pick 2-3 Web sites and view them in different ways (PC vs Mac vs cell phone vs WebTV, IE vs Netscape vs Opera vs AOL, Campus network (Ethernet to shared T1) vs business network (network to T1/T3) vs phone modem vs DSL vs cable modem, ???) Report on experience to appropriate Forum on CourseInfo. Comment on layout, colors, speed, anything else.