COVEN (Collaborative Virtual Environments) is a European project that seeks to develop a comprehensive approach to the issues in the development of collaborative virtual environment (CVE) technology. COVEN brings together twelve academic and industrial partners with a wide range of expertise in CSCW, networked VR, computer graphics, human factors, HCI, and telecommunications infrastructures. After two years of work, we are presenting the main features of our approach and results, our driving applications, the main components of our technical investigations, and our experimental activities. With different citizen and professional application scenarios as driving forces, COVEN is exploring the requirements and supporting techniques for collaborative interaction in scalable CVEs. Technical results are being integrated in an enriched networked VR platform based on the dVS and DIVE systems. Taking advantage of a dedicated Europe-wide ISDN and ATM network infrastructure, a large component of the project is a trial and experimentation activity that should allow a comprehensive understanding of the network requirements of these systems as well as their usability issues and human factors aspects.

In many large organizations, the model transformations allowing the engineers to more or less automatically go from platformindependent models (PIM) to platform-specific models (PSM) are increasingly seen as vital assets. As tools evolve, it is critical that these transformations are not prisoners of a given CASE tool. Considering in this paper that a CASE tool can be seen as a platform for processing a model transformation, we propose to reflectively apply the MDA to itself. We propose to describe models of transformations that are CASE tool independent (platform-independent transformations or PIT) and from them to derive platform-specific transformations (PST). We show how this approach might help in reaching a consensus in the RFP on MOF QVT, including a solution for the declarative/imperative dilemma. We finally explore the consequences of this approach on the development life-cycle.

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Distributed Virtual Reality systems are facing limitations due to the vast amount of streaming communications and world state update data to handle at host and network level. In order to lessen these burden, good mastering of data flows is required. Host information needs mostly depend on how local observers perceive the virtual world surrounding them. We propose a structure storing a hierarchical description of the world as a basis for host information needs identification. Our information rejection criterion is currently an approximation of the projected area along an axis toward the observer on a perpendicular plane. It can be applied to sources such as visual objects or sound sources. This structure, used to dynamically reference sources based on their position and scale, is called a spacescale structure (SSS); an octree is the actual storing structure. The SSS is traversed in order to retrieve sources, with respect to the rejection function. Optimizations of SSS traversal and SSS update for moving sources, based on temporal coherency, are presented here. A possible distributed architecture using our SSS is also proposed. This architecture makes use of multicast and client/server network topologies. The implementation of the SSS is evaluated locally in the context of large database culling.

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