Microsoft® .NET is the Microsoft XML Web services platform.

Microsoft application development is undergoing a major shift - a shift that will hopefully increase developer productivity and open the way for a new class of applications.

Currently, developers are building complex N-tier systems that integrate entire applications together from all over their networks. There is now a new shift enabled by the Internet - specifically the key Internet technology, XML. Whereas N-tier application development focused on building great applications for your corporation, XML is enabling the creation of great applications that can be used by anyone, anywhere. It increases the reach of applications and enables the continual delivery of software not so much as something you install from a CD, but as a service - a service like caller ID or like pay-per-view.

A Web service is an application that exposes its features programmatically over the Internet or intranet using standard Internet protocols like HTTP and XML. Think of it as component programming over the Web. The concept of distributing application logic over a network isn't new. The concept of distributing and integrating application logic over the Web is.

Web services are loosely coupled - where you can change the implementation at either end of a connection and the application will continue working. Technically, this translates to using message-based, asynchronous technology to achieve robustness, and using Web protocols such as HTTP, SMTP, and, most importantly, XML to achieve universal reach.

The key to making Web Services work across the Web is to agree to a simple data description format. That format is XML. Web Services require XML for three things: the basic wire format, service description, and service discovery. The 'Simple Object Access Protocol (SOAP)', an implementation of XML, is a set of rules describing how data and commands will be represented.

To implement such Web Services requires a suitable infrastructure. The .NET Framework provides that infrastructure. In the .NET Framework, all components can be Web services, and Web Services are just a kind of component. In effect, the .NET Framework takes the best aspects of COM (the Microsoft Component Object Model) and combines them with the best aspects of loosely-coupled computing.

The result is Microsoft's Web component system that simplifies programmer plumbing, deeply integrates security, introduces an Internet-scale deployment system, and greatly improves application reliability and scalability.

The .NET Framework consists of three main parts: the common language runtime, a hierarchical set of unified class libraries, and an advanced version of Active Server Pages called ASP.NET.

The .NET framework is an attempt to unify the disparate frameworks Microsoft has today. By creating a common set of APIs across all programming languages, the .NET Framework enables cross-language inheritance, error handling, and debugging.

ASP.NET builds on the .NET Framework's programming classes, providing a "Web application model" in the form of a set of controls and infrastructure that make it simple to build Web applications. Developers are exposed to a set of ASP.NET controls that encapsulate common HTML user interface widgets such as text boxes, drop down menus, and so on.

These controls actually run on the Web server, however, and simply project their user interface as HTML to a browser. On the server, the controls expose an object-oriented programming model that brings the richness of object-oriented programming to the Web developer.

Using ASP.NET Web Services features, ASP.NET developers can simple write their business logic and the ASP.NET infrastructure will be responsible for delivering that service via SOAP.