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Writing Web-based Client Applications

If you want to create Web-based clients for your multi-tiered database application, you must replace the client tier with a special Web application that acts simultaneously as a client to an application server and as a Web server application that is installed with a Web server on the same machine. This architecture is illustrated in the following figure.

There are two approaches that you can take to build the Web application:

- You can combine the multi-tiered database architecture with an ActiveX form to distribute the client application as an ActiveX control. This allows any browser that supports ActiveX to run your client application as an in-process server.
- You can use XML data packets to build an InternetExpress application. This allows browsers that supports javascript to interact with your client application through html pages.

These two approaches are very different. Which one you choose depends on the following considerations:

- Each approach relies on a different technology (ActiveX vs. javascript and XML). Consider what systems your end users will use. The first approach requires a browser to support ActiveX (which limits clients to a Windows platform). The second approach requires a browser to support javascript and the DHTML capabilities introduced by Netscape 4 and Internet Explorer 4.
- ActiveX controls must be downloaded to the browser to act as an in-process server. As a result, the clients using an ActiveX approach require much more memory than the clients of an HTML-based application.
- The InternetExpress approach can be integrated with other HTML pages. An ActiveX client must run in a separate window.
- The InternetExpress approach uses standard HTTP, thereby avoiding any firewall issues that confront an ActiveX application.
- The ActiveX approach provides greater flexibility in how you program your application. You are not limited by the capabilities of the javascript libraries. The client datasets used in the ActiveX approach surface more features (such as filters, ranges, aggregation, optional parameters, delayed fetching of BLOBs or nested details, and so on) than the XML brokers used in the InternetExpress approach.

Warning: Your Web client application may look and act differently when viewed from different browsers. Test your application with the browsers you expect your end-users to use.

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