ASP.NET is the next step in web development evolution with the Microsoft .NET framework. However, ASP.NET is not simply an update of syntax and function to its precursor-Microsoft ASP (Active Server Pages). ASP.NET introduces a completely new framework to web development on Microsoft operating systems. As you know from previous chapters HTML (Hypertext Markup Language), ASP, and most other web development schemes function based on a client/server model. In the web client/server model, historically all interaction consists of a transaction beginning with a request and ending with fulfillment. For example, the client, a web browser, contacts the server, a web- site, and requests information. The server then sends the information back to the client. Thus, the transaction is complete. The server has no more interaction with the client until the client sends another request for a transaction.
ASP.NET does not end the transaction when it fulfills the web browser request. Instead, ASP.NET relies on an event-driven model to actually monitor and respond to events that happen on the client, your web browser. How does a web server know what's happening in a web browser on your computer? ASP.NET uses client-side scripting to listen to events as they happen in your web browser.
To fully utilize ASP.NET and Dreamweaver MX, you need an understanding of the .NET framework, the syntax of VB.NET or C#, and the objects and underlying structure of ASP.NET technology. Obviously, this is well more than we can cover in one chapter, so we'll focus on an introduction to ASP.NET, the .NET framework and commonly used areas of VB.NET, and the C# language.
An ASP.NET script file is a text file (.aspx) that contains any combination of ASP.NET code and HTML code. The first time a web server processes an ASP.NET web page, the web server compiles the ASP.NET script file. Once compiled, the ASP.NET page is quick to respond to any subsequent web request. If the original ASP.NET script file is altered, the page is compiled again on the next page request. All ASP.NET script files are managed by the Common Language Runtime (CLR) environment.
CLR manages and compiles code on several levels. For example, the first time the web server processes an ASP.NET script file, the ASP.NET script file is compiled into a language called Microsoft Intermediate Language (MSIL). MSIL is an intermediate language that is essentially a compacted version of your ASP.NET script file. From that point, CLR compiles the MSIL code into machine code and processes it for web requests. Typically this process is almost instantaneous, but it occurs in the following steps.
A web browser requests a page at a specific web address, such as www.sybex.com.
The web server hosting the www.sybex.com website accepts that request. If the ASP.NET script file has been altered from the compiled version or has not been compiled, it is compiled into MSIL. It is then compiled again into machine code. The compiled version is executed, and HTTP responses are sent to the requesting browser.
The server forwards the HTTP request to the compiled version of the ASP.NET script file, which subsequently sends the resulting HTML to the requesting web browser.
This overview is just the tip of the iceberg. Unlike other web technologies, there is not one specific ASP.NET programming language. ASP.NET actually supports multiple programming languages. Although more language choices may develop, right now you can choose to develop in the VB.NET, C# (C Sharp), or JScript.NET language. (Dreamweaver MX supports only the VB.NET and C# programming languages, so that will be our focus throughout this chapter.) Also, since ASP.NET is built on the .NET technology, you have access to every powerful feature and function in the .NET framework.