Microsoft released the Domain-Specific Language tools as a technical preview [Download]. Using this graphical designer hosted in Visual Studio 2005, you can create the domain-specific concepts for a custom diagram designer. The underlying technology was used to create the Class Designer and Distributed System Designers in Visual Studio 2005.
This walkthrough shows how to create:
Concepts
Relationships
Include-relationships
Inheritance
More DSL information can be found here:
White papers: Walkthrough of the Microsoft Tools for Domain Specific Languages
Jochen Seemann's Blog: The first technical preview
DSL Tools Newsgroup
Report Bugs and Suggestions