The CLI, CTS, CLR, FCL, WPF, WCF, and WF
The .NET Framework starts with the Common Language Infrastructure (CLI). This is Microsoft's open specification for the core of the Microsoft .NET Framework. Since it's a specification, there is a clear rulebook that all .NET languages have to follow. And since they all do things the CLI way, they all have basically the same capability. It also means that language work together better too.
In fact Microsoft languages all compile into a new, lower level language called IL code. You can learn more about IL code, and the Microsoft program that you can use to work with it, in the About Visual Basic article ILDASM and the .NET Framework Tools.
The Common Type System (CTS) is another part of the .NET standardization. This part ensures that data types - like integers, strings, and many others - are defined the same way in the various languages supported by .NET. Just as an example, one of the more difficult problems in creating API calls to the Windows operating system in VB6 is creating a type that's easy to create in C++, the memory pointer.
The Framework Class Library (FCL) is at the center of it all. Basically, this is the library of software that all .NET languages use. It isn't everything that .NET can do, however. More programming is provided by other libraries like ADO.NET, ASP.NET, Windows Forms and lots of others. These libraries are updated maintained separatly so you don't have to make them part of your system if you don't need them, and so they can be updated without requiring an update to the whole Framework.
The Common Language Runtime (CLR) is the "engine" behind .NET that manages the execution of programs. In other words, When you execute your program, it's not actually your program that starts running. It's the CLR. But your program tells the CLR what needs to be done. That's why .NET programs are called "managed programs". The CLR doesn't let them do anything that they shouldn't be doing and cleans up after them too.
The CLR is Microsoft’s own implementation of an international standard, the Common Language Infrastructure (CLI) specification, that they also wrote. The CLI specification details how languages & libraries work together seamlessly both in development and execution environments.
The point here is that Microsoft has cooperated with making the CLI - the definition of what the CLR actually does - an international standard. But Microsoft's code for making it work is still owned by Microsoft. So anybody else can create their own "CLR" according to the standard and their stuff and Microsoft's should work together just fine. That's what the Mono Project is all about.
Framework 3.5
In version 3.5 of the .NET Framework, released in November 2007, three new libraries were added:
- Windows Presentation Foundation (WPF)
Microsoft says this gives you the abilty to create, "visually stunning user experiences on Windows clients." If you consider the Vista interface to be "visually stunning" then that's exactly right. But there's more than that. This library also supports "Tablet" input and adds new support for imaging, printing, accessibility, visualization, and automation.
- Windows Communication Foundation (WCF)
Communications has always been a "problem" because there were just so many different flavors. This new framework puts them all in one place and includes technologies such as transports, security systems, messaging patterns, encodings, network topologies, and hosting models. Microsoft has focused communications around web services in this library.
- Windows Workflow Foundation (WF)
This is one of the most innovative and potentially, one of the most useful additions to Framework 3.5. Workflow Foundation gives you the ability to write systems that model workflows like line of business applications, user interface page-flow, document-centric workflow, human workflow, composite workflow for service oriented applications, business rule driven workflow and workflow for systems management. This one is conceptually difficult but rich in possibilities.
On the next page, we dig into something that has been mentioned a lot, but never fully explored: Object Oriented Programming.
