The UML2 project (an Eclipse Tools sub-project) is an EMF-based implementation of the UML™ 2.x metamodel for the Eclipse platform. The objectives of this project are to provide a useable implementation of the metamodel to support the development of modeling tools, a common XMI schema to facilitate interchange of semantic models, test cases as a means of validating the specification, and validation rules as a means of defining and enforcing levels of compliance.

To get started you can view the "Getting Started with UML2" article.