Inter-service interoperability requires us to generalize the existing semantics of the services so that they can be composed with each other. As mentioned before, we will start with the Java model for defining objects. To define a general user interface model, we will assume that each applications is composed of semantic objects, which describe the semantic data being manipulated; view objects, which define the rendering of these objects on the screen; and subject objects, which define information about the subjects (e.g. name, job, etc), and for VE user interfaces, the positions and orientations of the subjects within a view, A hierarchy of semantic and view objects will be defined to cover the kind of bus clients we propose to support. For instance, we will define view objects that describe rooms within a building (to accommodate MUD/MOO-like use interfaces [ Curtis Social ] ). Our coupling model will be defined within this framework, allowing users to specify which of these these objects they wish to share (e.g. only the semantic objects, or semantic objects, view objects, and orientations of subjects; when changes to shared objects should be received or sent (e.g. when they make the change or when they enter or leave a room); which kinds of interactions are inconsistent (e.g. changing an object being viewed by another, being at the speaker's podium simultaneously); which kinds of accesses are not allowed (e.g. entering a private office); the information about other users in which they are interested (e.g. their names, their positions within a virtual space); and how they wish to start join sessions (e.g. when they are in the same room, or near each other in a VE).
Our support for real-time interaction will address both network reservation and operating system protocols. Resource reservation in a network is required to ensure reliable delivery of real-time multimedia streams over long distances. We propose to develop a framework for controlling the transmission of media streams via the independent manipulation of bit- and packet-rates. This framework will describe the capabilities of a media generating application as a set of bit-rate 4 message transmission-rate pairs called operating points. Each operating point for a stream will specify a bit and message-rate that the application is capable of generating. The framework characterizes the perceived network environment as a set of feasible operating points which is a subset of the full set of operating points. The elements of the feasible set are operating points which are sustainable under the current network conditions and result in the delivery of media streams with adequate throughput and latency for the application. The application will use feedback from the network to periodically estimate the set of feasible operating points. Based on these estimates, the current operating points is then selected for media transmission.
Our work on OS support is investigating a "new" process model based on the concept of rate-based execution (RBE) that addresses the requirements of this project. In an RBE system, processes specify their desired rate of progress in terms of the number of events they desire to process in an interval of specified duration. A process in an RBE system is guaranteed to make progress at at least its specified rate whenever work exists for the process. We conjecture that the notion of processing rate is a natural and useful abstraction for collaborative virtual environments and we propose to investigate this hypothesis in this project.
Our work on real-time support will take as input the coupling parameters selected by the users, which will determine the QOS (Quality of Service) provided by it. For instance, the processes and messages of users exchanging information incrementally will get precedence over those of users exchanging information on a daily basis.