The transformation schema: An extension of the data flow diagram to represent control and timing

The data flow diagram has been extensively used to model the data transformation aspects of proposed systems. However, previous definitions of the data flow diagram have not provided a comprehensive way to represent the interaction between the timing and control aspects of a system and its data transformation behavior. An extension of the data flow diagram called the transformation schema is described. This schema provides a notation and formation rules for building a comprehensive system model, and a set of execution rules to allow prediction of the behavior over time of a system modeled in this way. The notation and formation rules allow depiction of a system as a network of potentially concurrent `centers of activity' (transformations), and of data repositories (stores), linked by communication paths (flows). The execution rules provide a qualitative prediction rather than a quantitative one, describing the acceptance of inputs and the production of outputs by the transformations but not input and output values.