Web Pages with Features

Features on Web Pages Interactive Pages –Shows current date, get server’s IP, interactive quizzes Processing Forms –Serach a database, search engines, collecting info from users Pages with enhanced visual effects –Rollovers, animations. Dynamic Pages: –Dynamic Pages from material in a database –animations and dynamic images –popup windows, scrolling messages

Interactivity on a Web page can be achieved by: Using plug-ins with the browsers (Netscape) or ActiveX control (Internet Explorer). e.g., Shockwave Flash Player Using Programs either –Server-side programs or, e.g., CGI scripts, ASP, Server-side JavaScripts –Client-side programs e.g., Java Applet, Client-side JavaScripts

Server-side Programs: Server-side Programs run on the server Disadvantages: –only the system administrator could alter the program –1000s of users continually accessing the server, slowing it down and potentially overloading the system. Client-side Programs solve many of the problems by distributing the computing over the Web –Client-side Programs can be tested locally before uploading to the Web Server –However Client-side Programs can never completely replace Server-side Programs. e.g., searching a database on a central server.

Server-side Programs:

Client-side Programs:

Common Gateway Interface (CGI) CGI –A standard for interfacing applications with a Web server –Lets HTTP clients interact with programs across a network through a Web server –CGI applications Can be written in many different programming languages Reside in the directory /cgi-bin HTTP GET command –By issuing command, client directs server to send specific data to browser

Common Gateway Interface (CGI) CGI is an interface –Script or executable program must be used to interact with it Web browser –Take info from user –Using HTTP, sends info to a Web server –Server-side CGI program executed –Standard output from server-side applications or scripts redirected or piped to CGI –Output sent from CGI over the Internet to the client browser for rendering

Common Gateway Interface (CGI) Data path of a typical CGI-based application

Java Applet Applets are small applications to run on client’s machine. It is in separate file than the Web page itself. The downloaded applet executed by the browser’s built-in interpreter, that reduces the burden on the server. A Java applet first need to be compiled and needs JDK. JavaScript is a subset of Java and don’t need to be compiled, it is an interpreted only language.

JavaScript in Browsers Web browsers can interpret client-side JavaScript statements embedded in an HTML page. When the browser (or client) requests such a page, the server sends the full content of the document, including HTML and JavaScript statements, over the network to the client. The client reads the page from top to bottom, displaying the results of the HTML and executing JavaScript statements as it goes.

JavaScript on the Server On the server, you also embed JavaScript in HTML pages. The server-side statements can connect to relational databases from different vendors, share information across users of an application, access the file system on the server, or communicate with other applications through LiveConnect and Java. HTML pages with server-side JavaScript can also include client-side JavaScript. In contrast to pure client-side JavaScript scripts, HTML pages that use server-side JavaScript are compiled into bytecode executable files. These application executables are run in concert with a Web server that contains the JavaScript runtime engine. This makes creating JavaScript applications a two- stage process.

Development of Java In early 1990 programmers at Sun Microsystems began to develop an operating system to control appliances on the network using a language called Oak. In 1995, Oak was modified and renamed Java to use on the Internet. The programs written in Java need to compile to Byte Code first, which is machine code for a virtual machines, then run it using a platform dependant Interpreter. Independant Interpreters are available for different operating system. e.g., HotJava Recent Browsers incorporated Java interpreter.

JScript Jscript is a variation of JavaScript developed by Microsoft.