Beginning ASP.NET 4 in C# 2010 by Matthew MacDonald
Chapter 22. Component-Based Programming
Component-based programming is a simple, elegant idea. When used properly, it allows your code to be more organized, consistent, and reusable. It's also incredibly easy to implement in a .NET application, because you never need to use the Windows registry or perform any special configuration.
A component, at its simplest, is one or more classes that are compiled into a separate DLL assembly file. These classes provide some unit of logically related functionality. You can access a component in a single application, or you can share the component between multiple applications. Your web pages (or any other .NET application) can use the classes in your components in the same way they use any other .NET class. ...