io GPO WEEKNAPPLICATION DEVELOPMENT. — Pace 406 NPPLJED INTELLIGENCE Diasramming Methods Bring Precision to CASE lo0ols 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-atded 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 umentation is generated automatically ware engineer- The diagrams of the early "structured and thus does not slip out of date as ing, or ICASE, revolution" aren't good enough for this. changes are made. technology, in this earlier technology, the analyst Philosophers have often said that James Martin and designer had to use human intelli- what we are capable of thinking de- dtscusses 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. I-CASE tools processes are a form of language. With ing diagram need a complete, rigorous set of dia- computers, we may want to create pro- MARTIN speci fications gramming standards. cesses more complex than those we deloda 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 ill-conceived. 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, Hyperdiagram data-navigation diagrams, decision trees |ElY, ojespey MB and tables, state-transition diagrams and ['f' (Meze 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. Large, complex diagrams can be han- dled by means of zooming, nesting and windowing, among other technigues. The computer guickly catches errors and inconsistencies even in very large David Hannum sets of diagrams. Today, business, government and the military need highly complex and inte- Diagrams are aids to clear ideas. A poor choice can inhibit thinking. A good choice can speed JANUARY 16, 1989 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 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- tails of objects may be'displayed'in'win" | jo 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 of screen windows that are part of one hyper- diagram. The hyperdiagram can be ex- plored by pointing to objects or associa- tilons 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 hyperdiagram. The set of sereens in the figure illus- trates how diagrams are linked to form grated computer applications. The size si ei, hyperdiagrams. Each screen is part of a and oaplevdiy Of bobi arene work and improve the guality of the results. logicaliy consistent structure. Because too great for any hope of accuracy in di- a ea en | če e hyperdiagram contains links be- ; ing without aid de ai tween different types of representations IT nea alne su gneča Š nt- '— plex activities and procedures in dia- those processes. teni] ene these good CASE A ce pstaah e. grams than in text. A picture can be For someone developing a system de- over pa J r-oriented m fači RenOvance 4 the diagram, not the dlagrano it je worth much more than a thousand sign or program, the diagrams used are oa a a o enalvelo rocessible form. LE z: Ee ou pulario diagrams do not aids to clear ideas. A poor choice of dia: Next sie FU discuss the very heart pooramlla | ine Core cas and woolly think- — gramming technigue can inhibit think- ofan KCASF o an opre ado! ing common in textual specifications. ing. A good choice can speed work and pository. B prome grams that. ki aka pečka idla- — improve the guality of the results. a MINE t are p in meaning£x—me- When several people work on a sys- a TA PEL VARI RANI | ev chanical drawing, architects' drawings, — tem or program, the diagrams serveas am poe za adi Sred rovi piči Diagrams : manipulation by pi dapama za dis ectro | nics de- an essential communication tool. A for- terly, is available through High joke be Te a ine of thought procese. — and information engincenno sj eg — o esaming technigue is needed to ductivity Sofiogne [na of Marble ing, The analyst, designer, r s rna an engineering also need enable the developers to interchange head, Mass. (800). nc., of Marble- user and executive need a kn ins with standardized dia- — ideas and make their separate compo- mamo oč, o. 202 1200, For infor- gram types to assist in < BEE | se nents fit together with precision. 2 On semtnars, contact Tech- | though there are a host of — When systems are modified, clear dia Soogy Transfer Institute, 741 10h St, — a minimum number of ik | grams are an essential ajd te zaje. Santa Monica, Calif. 90402 (213) 394- to be learned, and | r nance. Thev | Ja menje 8305. In Europe, contact Savant, 2 mem sram (o understand how the program United Kingdom (0524) 739 505. | je JJ: