SADT : Structured Analysis and Design Technique

by jalal mjadli

As I wrote in the previous article, SADT (Structured Analysis and Design Technique) is a method that permits to analyze a system by dividing it to elementary functions to describe the technical solution to implement. It is useful to define user’s need for an  IT development, and also to describe the industrial processes and  procedures. In the present article, I’ll try to explain the concept of SADT.


It is a method that helps engineers to describe and understand systems, it can be used in many engineering fields

(Electrical, Electronics, Software…). It is based on the schematization of analysis in a top-down approach using boxes to represent entities and activities, and arrows to refer to the relations between entities. It allows to describe systems from global to more detailed levels. The basic element in this method is : Box + Arrows
Graphical construction
The analysis is done graphically and uses a decomposition with a top-down approach. To do this, we use box that should be in a determined context, and they are related to other boxes by arrows that represent constraints between them. The diagram can represent two models : data and activity.

Box is represented by a rectangle contains:

  • A verb to determine the activity
  • A label Aijk to mention the activity : Aijk is a child of Aij that is the child of Ai

Arrows can be incoming or outgoing:

  • Case activity model
    • Inputs enter from the left of box to represent data needed by the activity
    • Outputs exit from the right of box to represent results (the product) of activity
    • Controls from the top of box to represent constraints to accomplish activity, they are not consumed
    • Mechanisms to represent means and eventual tools to accomplish activity
  • Case data model, three types of arrows:
    • Inputs to represent activities to produce data
    • Outputs to represent consume the data
    • Controls to represent constraints influencing data

This following schema illustrates the concept:

The Controls and the Mechanisms are not required, they can be different or common. We can applicate this example to analysis many systems : Drink dispenser, Public Phone…

The big advantage of this method is its structured and hierarchical presentation that allows to decompose and analysis the complex systems, but it presents also some disadvantages : No presentation for the logical operators, and the sequences. It helped to give rise to other methods and it was implemented by different software.


© All rights are reserved to the author. Any use of this article is permitted in the context of teaching and non-profit activity.

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