Introduction to Visual Studio Data Designer Extensibility (by Milind Lele)

This whitepaper provides an introduction to Visual Studio Data Designer Extensibility (DDEX). In addition to providing a conceptual overview, it describes how different architectural components of DDEX work together, and shows how to accomplish common tasks when you implement a DDEX provider.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnvs05/html/ddexintro.asp