Server-side Scripts & Database Connectivity
 CIS311 Dr. Drew Hwang

Client-Server Interaction

• This type of client-server interaction involves three steps:

1. Getting the data from the client to the server.
2. Processing the data on the server.
3. Sending the results from the server to the client.

• CGI (Common Gateway Interface) scripts (or called server script) are the programs that run on the server to service client requests, and it is the standard for passing data from the browser to the server.
• The only difference between a regular program and a CGI scripts is where the data comes from. Whereas normal programs get their input directly from the user, or by reading local files, CGI scripts must get their input over the Internet through HTTP protocol.

Form-Script Interaction

• The <FORM> tag provides homepages with the most important script interaction. The complete syntax of the <FORM> tag when used for data input to the server is:
  <FORM ACTION=cgiURL METHOD=method>. The ACTION attribute specifies which CGI program on the server will process the input. The cgiURL is the location where the CGI program resides. Note that the CGI program may not even reside on the same server from which the page with the form was requested.
• When the user fills out the form and clicks the SUBMIT button (or sometimes called the "Search," the "Go", or the others), the user's browser then:

1. Picks the name of the script from the ACTION attribute.
2. Collects all the data from the various controls on the form and places them next to each other with the symbol & between them.
3. Generates the entire string that uses the format: cgiURL?data, where the data is a string that holds all the data entered by the user.

• After the server receives the string, it passes the entire string following the ? to the CGI program. The CGI program then processes the data and creates a new homepage with the results on the fly and sends it back to the server. Finally, the server sends the page back to the user's browser.
• The METHOD action specifies one of the two mechanisms for passing data to the server using GET or POST. With GET method, the string sent back from the client is stored in an HTTP server variable. With POST method, the data is presented as a name-value pair, where name is a control name on the form and value is its content (e.g., cgi-bin\orderin.exe?Itemno="COM244"&Orderqty="15"&...).
• Through using the <FORM> tag, the Web's client-server architecture provides a uniform interface for database front ends that can be used equally well in a local network environment, on an intranet/extranet, and on the Internet.

Server Applications Development

• Server-side applications can be written by using one of two supported interfaces, the server API (Application Programming Interface) or the CGI (Common Gateway Interface).
• A server API is an published interface that lets software developers write programs that become part of the Web server itself. Applications that use API are compiled as dynamic-link libraries (DLLs) that are loaded by the WWW service at startup. Because the programs are resident in memory, API programs are significantly faster than applications written to the CGI specification. In contrast, CGI scripts must be loaded and unloaded each time they are used, making the server processing time-consuming. However, CGI scripts are simple and portable across different computing platforms.
• There are three common-used server APIs including Microsoft's ISAPI, Netscape's NSAPI, and O'Reilly Web Site's WSAPI.

Internet Server Application Program Interface (ISAPI)

• ISAPI for Windows NT IIS can be used to write applications that Web users can activate by filling out an HTML form or clicking a link in an HTML page on your Web site. The remote application can then take the user-supplied information and do almost anything with it that can be programmed, and then return the results in an HTML page or post the information in a database (see the following figure).

• On Internet Information Server, the entire process of using the Internet Database Connector for this example is performed in six steps, as shown in the following diagram.

Common Gateway Interface (CGI)

• Common Gateway Interface (CGI) is a set of specifications for passing information between a client Web browser, a Web server, and a CGI application. A client Web browser can start a CGI application by filling out an HTML form or clicking a link in an HTML page on your Web server. As with ISAPI, the CGI application can take the information the client Web browser supplies and do almost anything that can be programmed, then return the results of the application in an HTML page, or post the information to a database. Because simple CGI applications are often written using scripting languages such as Perl, CGI applications are sometimes referred to as "scripts." The following figure illustrates how a browser, a server, and a CGI application exchange information by using CGI. The rest of this section discusses this five-part process.

Server Scripts Development

• For the most advanced Microsoft Web platform, server-side scripting using Active Server Pages uses the same VBScript language that is used in client-side scripting. The major difference is that with Active Server Pages, the script is placed in <%> tag and processed by the Web server before the Web page is sent to the client.

Client-side vs. Server-side Scripting

• Client-side scripting is great for animating Web pages and performing local data validation and computations, but large-scale client-server applications need additional functionality that requires the Web server to perform more complicated tasks.
• The advantages and disadvantages of client-side and server-side scripting*:

* Mike Morrison, et. al., "Using Microsoft Visual InterDev," QUE, 1997.

Sample HTTP Server Variables