The classic response is to specify the system to death. Produce reams of paper itemizing every requirement, tying down every unknown, and constraining the environment. Fire the gun using dead reckoning. One big calculation up front, then shoot and hope. Pragmatic Programmers, however, tend to prefer using tracer bullets.
Code That Glows in the Dark Tracer bullets work because they operate in the same environment and under the same constraints as the real bullets. They get to the target fast, so the gunner gets immediate feedback. And from a practical standpoint they're a relatively cheap solution. To get the same effect in code, we're looking for something that gets us from a requirement to some aspect of the final system quickly, visibly, and repeatably. Tip 15 Use Tracer Bullets to Find the Target
We once undertook a complex client-server database marketing project. Part of its requirement was the ability to specify and execute temporal queries. The servers were a range of relational and specialized databases. The client GUI, written in Object Pascal, used a set of C libraries to provide an interface to the servers. The user's query was stored on the server in a Lisp-like notation before being converted to optimized SQL just prior to execution. There were many unknowns and many different environments, and no one was too sure how the GUI should behave. This was a great opportunity to use tracer code. We developed the framework for the front end, libraries for representing the queries, and a structure for converting a stored query into a database-specific query. Then we put it all together and checked that it worked. For that initial build, all we could do was submit a query that listed all the rows in a table, but it proved that the UI could talk to the libraries, the libraries could serialize and unserialize a query, and the server could generate SQL from the result. Over the following months we gradually fleshed out this basic structure, adding new functionality by augmenting each component of the tracer code in parallel. When the UI added a new query type, the library grew and the SQL generation was made more sophisticated.