The Generic-Model Approach To Requirements Capture



It is generally recognised that it is the examination of the functional aspects of any requirement that leads to the greatest improvements in understanding as to the true nature of the system being specified. This is equally true during system specification as it is during any other phase of system development.

Because of the precise manner in which the G-MARC categorises all requirements into the different aspects that make up a specification it is very easy to select only the functional and performance aspects and then use only these to develop functional models at any level of detail. The G-MARC process for doing this (using only the original textual information) rapidly identifies those omissions and errors that normally impair the quality of a specification to a very marked extent.

The technique employed by G-MARC is to develop, largely automatically, a hierarchical set of dataflow diagram representations of the functional aspects of the specification and then, by animating these diagrams, identify improvements in the structure and in the performance information that the specification contains. Once developed this functionally correct structure is used as the framework upon which to 'hang' all the other aspects of the specification.

The use of Animation provides an extremely effective method for demonstrating the correctness of a specification - if it is not correct a model will not work! If the model does work it provides graphic and very easy-to-appreciate feedback, to the originator of the specification, as to the nature of the proposed functions and how they perform. The effect on performance of varying different requirements, can be readily investigated and, in this way required behaviour can be optimised - all without any design effort having been expended. What is more there are many situations where it is not possible to physically test the real system. The ability to test a simulated body of requirements embedded in a synthetic environment, and to rapidly identify the most demanding combinations of conditions, enables the G-MARC user to realise truly enormous cost savings during development and when final system testing is embarked upon.

Data flow diagrams are displayed in a manner that enables the Operator to inject a variety of event streams, at specified points, into any model according to an indefinite number of pre-configured scenarios.  Events traverse the data flow paths at speeds that are completely under the control of the Operator.  Via an Animation Clock the Operator is able to slow down or speed up the rate of animation of the model dependent upon the nature of his interests.  The animation may be halted at any time - to enable the state of any process to be examined - and then allowed to continue.  Comprehensive model instrumentation facilities are provided which enable any point in a model to be monitored and the associated activity recorded.   The entire process is controlled by means of a flexible test-bed that can be rapidly configured for each model and any associated scenario and stopped and/or started as many times as required, with all inputs and/or outputs being continuously logged for later analysis.

All of the above facilities are provided with the primary aim of supporting the elimination of incompleteness and error in the information contained in a requirements specification - thus providing the client organisation with an easy-to-comprehend overview of the behaviour of the system that has been specified and immediate feedback of possible problems.