IDRIS - INTERACTIVE DESIGN OF REACTIVE INFORMATION-SYSTEMS

The IDRIS project is developing a model, a methodology, a notation, and a CASE tool for the interactive design of real-time, or reactive, systems. Increasingly such designs are implemented on parallel hardware, for performance and reliability reasons. The work described here addresses performance, but not reliability, issues. The model describes a real time system in terms of a database and a set of asynchronous tasks. Each task is the system's response to an external stimulus event. A task decomposes into atomic transactions, acting on entities in the database, connected by a control structure which is determined by entity access constraints. Based on a static analysis of these data dependencies, the methodology is able to rely on scheduling rather than conventional locking to control access to the database. The model describes real time systems generally. The methodology concentrates on the class of hard real time systems designs - those which must guarantee to meet the response latency and throughput constraints specified by the requirements. The methodology uses scheduling and allocation heuristics to map tasks and their transactions onto physical processors. The methodology has a number of stages and the designer is assisted by four graphical notations: event context diagrams; data dependency rings for capturing both intra task and inter task data dependencies; precedence graphs for expressing the intra task control structure implied by the data dependencies; Gantt charts for expressing worst case schedules. The methodology assumes a run time environment with a hierarchy of schedulers to control processing and access to data entities. An interactive CASE tool helps the designer capture and manipulate the design information, display partial designs, and perform allocation and scheduling trials against the specification. An example real time system design, for a ship control system, generated using the methodology and the CASE tool, is briefly described.