Requirements modeling for embedded realtime systems
MBEERTS'07 Proceedings of the 2007 International Dagstuhl conference on Model-based engineering of embedded real-time systems
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The next article, by Ross and Schoman, is one of three papers chosen for inclusion in this book that deal with the subject of structured analysis. With its companion papers --- by Teichroew and Hershey [Paper 23] and by DeMarco [Paper 24] --- the paper gives a good idea of the direction that the software field probably will be following for the next several years. The paper addresses the problems of traditional systems analysis, and anybody who has spent any time as a systems analyst in a large EDP organization immediately will understand the problems and weaknesses of "requirements definition" that Ross and Schoman relate --- clearly not the sort of problems upon which academicians like Dijkstra, Wirth, Knuth, and most other authors in this book have focused! To stress the importance of proper requirements definition, Ross and Schoman state that "even the best structured programming code will not help if the programmer has been told to solve the wrong problem, or, worse yet, has been given a correct description, but has not understood it." In their paper, the authors summarize the problems associated with conventional systems analysis, and describe the steps that a "good" analysis approach should include. They advise that the analyst separate his logical, or functional description of the system from the physical form that it eventually will take; this is difficult for many analysts to do, since they assume, a priori, that the physical implementation of the system will consist of a computer. Ross and Schoman also emphasize the need to achieve a consensus among typically disparate parties: the user liaison personnel who interface with the developers, the "professional" systems analyst, and management. Since all of these people have different interests and different viewpoints, it becomes all the more important that they have a common frame of reference --- a common way of modeling the system-to-be. For this need, Ross and Schoman propose their solution" a proprietary package, known as SADT, that was developed by the consulting firm of SofTech for which the authors work. The SADT approach utilizes a top-down, partitioned, graphic model of a system. The model is presented in a logical, or abstract, fashion that allows for eventual implementation as a manual system, a computer system, or a mixture of both. This emphasis on graphic models of a system is distinctly different from that of the Teichroew and Hershey paper. It is distinctly similar to the approach suggested by DeMarco in "Structured Analysis and System Specification," the final paper in this collection. The primary difference between DeMarco and Ross/Schoman is that DeMarco and his colleagues at YOURI]DN inc. prefer circles, or "bubbles," whereas the SofTech group prefers rectangles. Ross and Schoman point out that their graphic modeling approach can be tied in with an "automated documentation" approach of the sort described by Teichroew and Hershey. Indeed, this approach gradually is beginning to be adopted by large EDP organizations; but for installations that can't afford the overhead of a computerized, automated systems analysis package, Ross and Schoman neglect one important aspect of systems modeling. That is the "data dictionary," in which all of the data elements pertinent to the new system are defined in the same logical top-down fashion as the rest of the model There also is a need to formalize mini-specifications, or "mini-specs" as DeMarco calls them; that is, the "business policy" associated with each bottom-level functional process of the system must be described in a manner far more rigorous than currently is being done. A weakness of the Ross/Schoman paper is its lack of detail about problem solutions: More than half the paper is devoted to a description of the problems of conventional analysis, but the SADT package is described in rather sketchy detail. There are additional documents on SADT available from SofTech, but the reader still will be left with the fervent desire that Messrs. Ross and Schoman and their colleagues at SofTech eventually will sit down and put their ideas into a full-scale book.