Software Prototyping

A software prototype is a live, working system; it is not just an idea on paper. Therefore, it can be evaluated by the designer and eventual users through its use in an operational mode. It performs actual work; it does not just simulate that work. It may become the actual production system or it may be replaced by a conventionally coded production system. Its purpose is to test out assumptions about users' requirements, about the design of the application, or perhaps even about the logic of a program.

A prototype is a software system that is created quickly—often within hours, days, or weeks—rather than months or years. With only conventional programming lan­guages, such as COBOL, it was much too expensive to create both a prototype and a production version. Therefore, only production systems were developed. With end user tools, people can get prototypes up and running quickly. The prototype is relatively inexpensive to build because the language creates much of the code.

Prototyping is an iterative process. It begins with a simple prototype that performs only a few of the basic functions. Through use of the prototype, system designers or end users dis­cover new requirements and refinements to incorporate in each succeeding version. Each version performs more of the desired functions and in an increasingly efficient manner.

Both software prototyping and 4GLs have proven to be significant underpinnings for the present software application development world. To demonstrate a dramatic use of both a 4GL and prototyping, we describe work at Santa Fe Railway in the early 1980s. Their use of a 4GL was unique because it took the opposite approach of just about everyone else. Most companies used 4GLs for management reports and end user applications, that is, as a sideline from their operational systems. Santa Fe, on the other hand, used the 4GL for their operational system and left the management reporting in COBOL. Their approach, using today's tools, would be just as unique. The reasons for their unusual decision are made clear in the case example.

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