IDI Course SA-05
System Modeling


2 half-day sessions + optional half-day workshop

Designed for:

  1. Systems analysts developing requirements and functional specifications for new applications.
  2. Senior programmers and designers who will translate a system model into an internal system design.

Note that user representatives participating in a system development project should not need to take a course in how to interpret a system model. A good system model based on the techniques of this course should be intuitively understandable by an non-technical audience.


We first review criteria for understandability of a system specification by its intended audiences, observing that the central component of an external system design has to show the relationships among all the other components. We then discuss how well the following satisfy those criteria:

We conclude that the dataflow diagrams pioneered by DeMarco, Gane & Sarson, and others, are a suitable foundation, but that alternatives can sometimes supplement or replace them.

We begin looking at a case study, starting with the so-called " context diagram". We present mainstream graphic conventions for representing each system element in a simple and intuitively obvious (to the reader) way.

Depending on the participants' interests and backgrounds, we may ask teams of 3 or 4 to develop a 3-level model of some system that interests them.

We then consider DeMarco's recommended sequence of modeling, showing how an examination of an old or existing application system can lead logically to a specification for a new one.

Throughout the course we strongly emphasize criteria for determining when additional detail is required and what forms that detail ought to take. We give some widely-accepted rules and criteria for analyzing multi-level dataflow diagrams.

Finally, we survey computer-based tools for preparing and maintaining system models.

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