INTRODUCING ASP.NET

With .NET, Microsoft has completely redesigned ASP to address its limitations. To accomplish this task, backwards-compatibility with ASP had to be sacrificed. As we will see, migrating ASP scripts to the managed environment is not always a straightforward task. Since ASP is in such wide use, however, Microsoft ensured that ASP scripts execute without modification on a machine with the .NET Framework (the ASP engine, ASP.DLL, is not modified when installing the .NET Framework). Thus, IIS can house both ASP and ASP.NET scripts on the same machine. Among the advantages ASP.NET boasts over ASP are the following:

1. Separation of code from content. ASP.NET allows the developer to separate script code from HTML. This allows for a clean separation of code from content and formatting and promotes code reuse.

2. Support for compiled languages. While ASP.NET still supports the traditional set of scripting languages, support is also provided for fully compiled languages. Instead of using VBScript, a developer can use VB.NET and access features such as strong typing and object-oriented programming. Using compiled languages also means that ASP.NET pages do not suffer the performance penalties associated with interpreted code. ASP.NET pages are precompiled to byte-code and Just In Time (JIT) compiled when first requested. Subsequent requests are directed to the fully compiled code, which is cached until the source changes.

3. Greater support for different browsers via server-side controls and events. Following object-oriented design principles, ASP.NET pages make use of server-side controls called ASP.NET web controls. These controls are instantiated on the server, and like regular objects they have associated methods, properties, and events. The advantage of server-side controls is that they render themselves on the client as standard HTML 3.2 (and optionally DHTML), depending on the capabilities of the client browser. In other words, an advanced browser will automatically receive advanced features, while an older browser will still receive readable HTML. Since the controls reside completely on the server and send standard HTML to the client, browsers can be completely unaware of the .NET Runtime. Thus, virtually any browser can access an ASP.NET page.

4. Intuitive GUI design. With ASP.NET you can design web applications as you did in Visual Basic 6, by dragging and dropping GUI elements in a sophisticated design environment. The next topic in this chapter demonstrates this feature. As you will see throughout this chapter, almost every new feature introduced with ASP.NET is designed to provide tremendous improvements for rapid web application development. The advanced GUI design, separation of code from content, encapsulation of HTML, and masking of client-side/server-side issues makes ASP.NET a very powerful platform for designing web pages.