Department of Information Engineering 1 What is –Java? –Javascript –VisualBasic –CGI –NT –Linux –Unix

Department of Information Engineering 2 Some jargons about Internet What is a server? What is a client? What is a browser? What is HTML? What is the limitation of HTML?

Department of Information Engineering 3 Scenario –A student is browsing a web site for selling books –the student moves the mouse pointer to a button, the button changes color –the student clicks the mouse button, a form appear –the student fills in the form, the visa card number, and press the button finish –the data is sent to the web site for further processing

Department of Information Engineering 4 How to make the button changes color when the mouse pointer is over the button? –Need a smart program at the client side to monitor the position of the mouse pointer –client side programming What is it? –Program that is run at the client side The other approach is server side programming –program is run at the server side

Department of Information Engineering 5 Client side programming –HTML is just a markup language support formatting and layout of a document not a programming language what is a programming language? –Can control the flow of execution, such as if the pointer is over the button, do this if the pointer is clicked, do that if the pointer is moved away from the button, do that

Department of Information Engineering 6 The program –how the client obtains the program javascript –pass together with the html file –the browser is able to understand the program and execute it –supported by both Netscape and IE –you have already written some javascript using Dreamweaver !!

Department of Information Engineering 7 Tom.com homepage function MM_swapImgRestore() {... body { font-family: Arial, Helvetica, sans-serif }.. <table border="0" cellspacing="0"... standard HTML table

Department of Information Engineering 8 Compare the code in tom.com and the one you have written in Dreamweaver –the structure is almost the same function... –contains the program –this is the program that swap the image when your mouse is over it you have also set the style of the text using Dreamweaver

Department of Information Engineering 9 Limitation of Javascript –a small language with limited control –sufficient for providing nice web pages What is Java? –Java is very different from Javascript –the similarity of the name is due to marketing consideration –it is a full-fledge programming language –java is also supported by Netscape and IE –client downloads the Java program called Applet, and run as a program at client side

Department of Information Engineering 10 What else can be run at client side? Plug-in –different from Javascript and Java, the program is supported by the computer system, not by the browser –basically download a program and run –the code is not interpreted by the browser

Department of Information Engineering 11 Example Powerpoint –if browser downloads a file with extension.ppt –the Powerpoint program is called Real Audio if a file with extension.ram is downloaded, –the Real Audio program is called Macromedia Flash –for animation (e.g. IT courseware of CUHK) –if a file with extension.swf is downloaded, the Flash program is called

Department of Information Engineering 12 Now, what happen if we submit a form from the browser? –The browser sends the text you entered to a program in the server The program at the server side must process your request, like any other program this is called server side programming Example: CGI, ASP (from Microsoft)

Department of Information Engineering 13 what is the difference between NT/Linux/Unix servers? –These are the most common platforms used for Internet applications NT - product from Microsoft look the same, feel the same as Window 98, so what is the difference? –NT can serve multiple users simultaneously –Window is designed for single user

Department of Information Engineering 14 What is Unix? –developed in AT&T about 30 years ago –supports multiple users –was freely distributed at that time –used by many universities in early 80s –bundles the TCP/IP software –because Unix was used by many universities, TCP/IP became the standard networking software –most commercial grades servers are based on Unix –not novice-friendly

Department of Information Engineering 15 What is Linux? –Software developed by a student named Linus Torvalds from Finland(?) in early 90s –originally meant to be an exercise, try to understand computer system by writing a Unix-like system –later on developed into an Internet-based world-wide collaboration by many top notched programmers –modern freeware open-source movement –freely distributed, loosely supported worldwide by hobbyists