We advocate the approach of integrating a collection of function-specific tools into a distributed and extensible environment, where tools can easily use facilities provided by other tools. Isolation of functionality makes the environment modular, and makes tools easy to develop and maintain. Distribution lets us benefit from the cumulative computation power of workstation clusters. Tool-level cooperation allows us to exploit the commonality that is inherent to many scientific manipulation systems. An enabling infrastructure of communication and interaction tools, display and visualization facilities, symbolic processing substrates, and simulation and animation tools saves avoidable re-implementation of existing functionality, and speeds up the application development.
The Shastra environment consists of multiple interacting tools. Some tools implement scientific design and manipulation functionality (the Shastra Toolkits). Other tools are responsible for managing the collaborative environment (Kernels and Session Managers). Yet others offer specific services for communication and animation (Service Applications). Tools register with the environment at startup, providing information about the kind of services that they offer (Directory), and how and where they can be contacted for those services (Location). The environment supports mechanisms to create remote instances of applications and to connect to them in client-server or peer-peer mode (Distribution). In addition, it provides facilities for different types of multi-user interaction ranging from master-slave blackboarding (Turn Taking) to synchronous multiple-user interaction (Collaboration). It implements functionality for starting and terminating collaborative sessions, and for joining or leaving them. It also supports dynamic messaging between different tools. Tools are thus built on top of the abstract Shastra layer. The architecture of the system is depicted below:
Collaborative Sessions, or Sessions, are instances of synchronous multi-user collaborations or conferences in the Shastra environment. A collaboration in Shastra consists of a group of cooperating tools regulated by a Session Manager, the conference management tool of Shastra. One Session Manager runs per collaborative session. It maintains the session and handles details of connection and session management, interaction control and access regulation. It keeps track of membership of the collaborative group, and serves as a repository of the shared objects in the collaboration. It supports a multicast facility needed for information exchange in a synchronous multi-user conferencing scenario. It has a constraint management subsystem that resolves conflicts that arise as a result of multi-user interaction, enabling maintenance of mutual consistency of operations. It has a regulatory subsystem that controls synchronous multi-party interaction, and provides a floor control facility based on turn-taking. Every Session Manager implements functionality to service the following session control requests. The Information Flow in the Shastra Environment is shown in the following Figure.
