Towards Execution Models of Distributed Systems: A Case Study of Elevator Design

Many of United Technologies' products contain or will soon contain a distributed network of processors. In order to explore issues related to designing such systems, two different methods of modeling system functionality have been applied to a simplified elevator controller. One method results in data flow oriented models which are executable within a context of the association of units of functionality with distributed processors. Execution thus produces processing and communication workloads which can be used for design analysis. In order to allow rapid assessment f alternative designs, an automated approach was developed which allowed the units of allocated functionality to be arbitrarily fine. However, neither the data flow approach not this automated allocation handle the complexity of large models sufficiently well. A similar elevator model has been defined with a technique which combines object-oriented analysis with formal specification. This combination avoids unnecessary complexity yet allows the model to have a formal semantics, which is necessary (bit not sufficient) to achieve the key methodological requirement of executability. Future work will integrate the object-oriented and data-flow approaches into a framework which supports specification, automated fine-grain allocation, and execution for large models.