Issue No. 02 - Feb. (1986 vol. 12)
Paul T. Ward , Yourdon, Inc., New York, NY 10036
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. This paper describes an extension of the data flow diagram called the transformation schema. The transformation 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. The transformation schema permits the creation and evaluation of two different types of system models. In the essential (requirements) model, the schema is used to represent a virtual machine with infinite resources. The elements of the schema depict idealized processing and memory components. In the implementation model, the schema is used to represent a real machine with limited resources, and the results of the execution predict the behavior of an implementation of requirements. The transformations of the schema can depict software running on digital processors, hard-wired digital or analog circuits, and so on, and the stores of the schema can depict disk files, tables in memory, and so on.
Delay, Data models, Production, Buffer storage, Transforms, Automata, transformation schema, Concurrent systems, data flow diagram, requirements modeling, software design, systems design
P. T. Ward, "The transformation schema: An extension of the data flow diagram to represent control and timing," in IEEE Transactions on Software Engineering, vol. 12, no. , pp. 198-210, 1986.