From the webpage:
Roles are about objects and how they interact to achieve some purpose. For thirty years I have tried to get them into the into the main stream, but haven’t succeeded. I believe the reason is that our programming languages are class oriented rather than object oriented. So why model in terms of objects when you cannot program them?
Almost all my documents are about role modeling in one form or another. There are two very useful abstractions on objects. One abstraction classifies objects according to their properties. The other studies how objects work together to achieve one or more of the users’ goals. I have for the past 30 years tried to make our profession aware of this important dichotomy, but have met with very little success. The Object Management Group (OMG) has standardized the Unified Modeling Language, UML. We were members of the core team defining this language and our role modeling became part of the language under the name of Collaborations. Initially, very few people seemed to appreciate the importance of the notion of Collaborations. I thought that this would change when Ivar Jacobson came out with his Use Cases because a role model shows how a system of interacting objects realizes a use case, but it is still heavy going. There are encouaging signs in the concept of Components in the emerging UML version 2.0. Even more encouaging is the ongoing work with Web Services where people and components are in the center of interest while classes are left to the specialists. My current project, BabyUML, binds it all together: algorithms coded as classes + declaration of semantic model + coding of object interaction as collaborations/role models.
The best reference is my book Working With Objects. Out of print, but is still available from some bookshops including Amazon as of January 2010.
You can download the pdf of Working with Objects (version before publication). A substantial savings over the Amazon “new” price of $100+ US.
This webpage has links to a number resources from Trygve M. H. Reenskaug on role modeling.
I saw this reference in a tweet by Inge Henriksen.