Just What Is a Web Application?

Before I go any further, I ought to explain just what I mean by a "Web application." A Web application is an application that runs on a Web server and is accessed at the client end using an Internet browser program or other program with Web browsing facilities. In this model, all the processing in the application is performed on the Web server and the client receives HTML-coded pages that contain the user interface and client data. Of course, real-world applications contain a mixture of server-side and client-side processing. Browsers can download Microsoft ActiveX components and Java applets to add richer functionality to the interface of the application. Web pages can contain scripting code to run at the client end to provide further flexibility in the front end and preprocessing of data and requests for the back end.

The Web application model offers the prospect of a single client front end that is capable of accessing a variety of different applications on a remote server. While this front end might not be the thinnest client in the world, it can be a fairly universal client. This client could also be updatable remotely. If it doesn't have a particular capability required by an application (such as the display of a particular format of data), the client could download a component that it can use to give it that capability. Similarly, the versions of components the client already has could be checked to ensure that they are always up to date.

A Web application in the corporate intranet obviously is attractive for a variety of reasons. By having a single client application for all server applications, rollouts are simplified and client PC maintenance costs are reduced. Standard machine setups can be used with the client gradually updating itself as it accesses different applications. In the corporate environment, where there can be tight control over the software on a user machine, applications can be produced for a specific browser, thus allowing developers to fully exploit the capabilities of that browser. Web applications also allow people to work from home or away from their normal office location without losing functionality.

Developing applications for the Internet means you have a huge audience that can access your work. Unlike the corporate intranet environment, you can no longer assume that all browsers accessing your application will have the same capabilities, but this is by no means a barrier to deploying applications over the Internet.

IIS or ASP?

Before the IIS Application template was introduced to Visual Basic, developers wanting to produce Web applications had Active Server Pages (ASP) technology available to them. The ASP model allowed developers to write pages that could be accessed from a browser and that performed some processing on the Web server before returning HTML to the browser. The server-side code could be written in a variety of languages (including client-side scripting languages, such as VBScript or Microsoft JScript), so long as the server had access to a scripting engine for that language. ASP provides a number of different objects for server scripts that allow interaction with both the client and the server.

IIS applications, while based on ASP, provide a better way for Visual Basic developers to produce Web-based applications. For example, the development environment is familiar (though there are differences for IIS application development, as you'll see). The language is the same, so you don't have to learn a new scripting language. The processing code and visual interface code can be separated out to provide a cleaner project—ASP pages have script and interface code intermingled. Visual Basic is also a much more powerful language in which to develop applications than is a scripting language (even if the scripting language can call on code components to perform any tricky processing).

At the time of this writing (on the March beta of Visual Studio 6), there is some MSDN documentation on developing IIS applications but no example code (apart from the fragments appearing in the documentation). So, while I'm not flying completely blind on this one, let's say there're some low clouds and all I have are the instruments to guide me (plus a sick bag and spare underwear!).