s PO WEEKN APPLICATION DEVELOPMENT Pace 46 JANUARY 16, 1989 APPLIED INTELLIGENCE Diasramming Methods Bring Precision to CASE Tools be as obvious as possible. mation collected in a centralized ency- In this, the The diagrams must be sufficiently clopedia when the diagrams are drawn). second of a six- complete and rigorous to serve as a ba- When changes are made to systems, the part series on sis for .code generation and for automat- diagrams are changed on the screen, and integrated com- | ic conversion of one type of diagram the code is regenerated. The design doc- puter-aided soft- into another. umentation is generated automatically ware engineer- The diagrams of the early "structured.'— and thus does not slip out of date as ing, or I-CASE, revolution" aren't good enough for this. changes are made. a technology, In this earlier technology, the analyst Philosophers have often said that Š James Martin and designer had to use human intelli- what we are capable of thinking de- | Li discusses the gence to bridge gaps between one type pends on the language we use for think- | CASE tool func- of diagram and another, and they often ing. The diagrams we draw of complex tion of convert- made mistakes in doing so. CASE tools JAMES | ing diagram need a complete, rigorous set of dia- computers, we may want to create pro- | MARTIN specifications gramming standards. cesses more complex than those we directly into op- With appropriate diagramming tech- would perform manually. Appropriate | erational code. nigues, it's much easier to describe com- diagrams help us to visualize and invent. The evolution of diagramming has picked up staggering speed in the last, few years. Not long ago, systems ana- lysts drew their diagrams with pencils and erasers. Hand-drawn diagrams often grew very large, straggling across white boards or pasted onto large sheets of paper. And a design freguently consisted of multiple binders of nested data-flow diagrams and structure charts. These binders were usu- ally fraught with inconsistencies and omissions. What's more, the diagrams were sloppy and the diagramming tech- nigue ilkconceived. CASE tools bring to diagramming a method for enforced precision. A good CASE tool uses diagram types that are precise and computer-checkable. Among the diagram types used by CASE tools implementing an informa: tion-engineering methodology are decom- position diagrams, dependency dia- grams, data-flow diagrams, action dia- grams (for specification of procedures), data-analysis diagrams, data-structure diagrams, entity-relationship diagrams, data-navigation diagrams, decision trees and tables, state-transition diagrams and dialogue-design diagrams. (CASE tools that support a software- engineering methodology use a subset of these diagram types: chief data-flow dia- grams, decomposition diagrams and enti- ty relationship diagrams. spe: beli zr diagrams can be han- means of zooming, nesting and windowing, among other technigues. The computer guickly catehes errors and inconsistencies even in very large sets of diagrams. Today, business, government and the military need highly complex and inte- grated computer applications. The size and complexity of these applications are Diagrams are aids to clear ideas. A poor choice can inhibit thinking. A good choice can speed work and improve the guality of the results. processes are a form of language. With David Hannum works and then to design changes. When a change is made, it often affects other parts of the program. Clear diagrams of the program struc- ture enable maintenance programmers to understand the conseguences of the changes they make. When debugging, clear diagrams are also highly valuable tools for understanding how the pro- grams ought to work and for tracking down what might be wrong. Diagramming, then, is a language, es- sential both for clear thinking and for human communication. An enterprise needs standards for its information-sys- tems diagrams, just as it has standards for engineering drawings. A diagram | and its associated information in a CASE tool can be very different from a li diagram on paper. Paper constrains the diagram to two dimensions. With a computer, many different rep- resentations of the design can be linked together logically. For example, the same block may appear on both a data- flow diagram and a decomposition dia- gram. Data access on an action diagram must relate to information specified on an entity-relationship diagram or in a data model. The inputs and outputs to a procedure represented by an action must be the same as those on the corre- sponding data-flow diagram. Linking Diagrams Together The terms "hyperdiagram" or "hyper- chart' describe a representation of plans, models or designs in which many two-dimensional representations are log- ically linked together. A simple hyper- diagram is a diagram in which the de- J tails of objects' may be'displayed'in win | dows. A more complex hyperdiagram uses many types of two-dimensional dia- grams. A block or a line may be dis- played in a window as text, as a fill-in- the-blanks form, an action diagram, a matrix or a different type of diagram. The figure shows a family o£ screen windows that are part of one hyper- diagram. The hyperdiagram can be ex- plored by pointing to objects or associa- tions and displaying details of them. An [CASE tool kit gives the implementor the facilities to explore or to build the hyperdiagram. The tool should enforce consistency within the h; li k The set, of screens in the figure illus- trates how diagrams are linked to form hyperdiagrams. Each screen is part ofa logically consistent structure. Because the hyperdiagram contains links be- tween different types of representations — o EO plex activities and procedures in dia- grams than in text. A picture can be worth much more than a thousand words. Computerized diagrams do not and enforces consistency among these representations, it's a major advance over paper-oriented methods of analysi and design. z Next week, Tll discuss the very heart those processes. For someone developing a system de- sign or program, the diagrams used are aids to clear ideas. A poor choice of dia- allow the sloppiness and woolly think- grammin; ibi č helps kate! a design, a kg neza paii ing aa Saj (da psdčesle! ing. A A a ak, ; O AE bi. a miro ev another deliverable segmen types use formal dia- improve the guality of th oa re o process in such a way that it grams that are en: W A o ka pleve precise in a me- When several people work o: - i ivii validated seetianlat Ctaricl dravinga, aetitci' drawinga, | tem or program, ine dlagramna serve zs za ana ai ae, diagrams, z essential pe oncada tol A for. | terly, is available through High pie diagramming technigue is needed to ducti Ine., of Marble- grabi nika developers to ini head, Mass. (800) 242. iso For infor: Kosa s make their separate compo- mation on contact Tech- together ime - nology Transfer Institute, 741 10th Him omena motineh le dear dia- Santa Monica, Calif. 90502 (213) 394. grams sonia pale ei ZE In Europe, contact Savant, 2 Jame nev make Dobe ew St, Carnforth, Lancs., LA5 9BX United Kingdom (0524) 734 505.