Today's high-level synthesis systems provide means to solve complex design problems but leave the user alone with an increasing number of difficult design decisions. We introduce a user model derived from requirements resulting from discussions with users and examination of existing systems. An implementation of this user model based on an existing high-level synthesis environment is sketched. IntroductionCurrent frameworks and design systems administrate team work by providing intricate access and concurrency control mechanisms. In these models, the user is seen as an isolated person communicating with others exclusively through the use of common design objects. This view does prevent data collisions but it does not support human interaction in a working environment. Experience shows that good communication in a design team, the sharing of knowledge and results, increases work efficiency but on the other hand, people tend to work out a problem for themselves instead of asking a colleague who might already have found a solution. It follows that a design environment which takes user communication into account should provide means to share and distribute user experience within the system. This becomes increasingly important in high-level synthesis systems that require a lot of user interaction and expert knowledge in optimization steps. We propose a user model introducing the concept of virtual roles to satisfy the need for communication between users in design frameworks. Our model is based on a small design team of up to eight people. Many state-of-the-art synthesis environments are tailored for single-user utilization, assuming a user that is well versed in all aspects of design. This is unrealistic -it is more likely that several people will pool their knowledge to achieve a design goal. On the other

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