Trademark (structured analysis and design technique) A method for modelling complex problems and systems, developed by Douglas Ross in the mid- 1970s. Although SADT is a general- purpose modelling tool, it is particularly effective for requirements definition for arbitrary systems problems and is widely used for this purpose in the software engineering field. SADT can be viewed as having three main parts: a set of methods that can assist an analyst in gaining an understanding of a complex system, a graphical language that can be used to record and communicate that understanding, and administrative guidelines that contribute to the orderly progress of the analysis and early detection of problems.

The methods of SADT are based upon several concepts. Top-down decomposition allows information to be dealt with at progressive levels of detail. Model-building both assists understanding and permits communication of that understanding. Adoption of a variety of complementary viewpoints allows all relevant aspects of a system to be considered while limiting consideration at any time to one well-defined topic. The dual ‘things’ and ‘happenings’ aspects of any subject are used to reinforce understanding and promote consistency. Review and iteration procedures ensure the quality of the model that is developed.

The graphical language of SADT consists basically of boxes and arrows that are used to construct SADT diagrams. The language is concerned only with the structured decomposition of the subject matter, and any other language (e.g. natural language) can be used within the boxes and to label the arrows. A single SADT diagram may model either processes or data. A diagram that models processes, called an actigram, uses boxes to show the individual processes and uses arrows to show dataflows between processes, any constraints that apply, and the mechanisms for carrying out the processes. The arrows entering and leaving a box serve to bound the context of the process, and this can then be decomposed on further actigrams through successive levels of detail to any level required. Similarly the corresponding data decomposition is presented in datagrams and consideration proceeds from highly abstract data objects through successive levels of decomposition and definition.

The administrative guidelines of SADT provide among other things for independent review of the diagrams as they are produced and for configuration control of the emerging model.

A nonproprietary form of SADT developed by the US Air Force is now available and is known as IDEF.