Real World Instrumentation with Python

Requirements

Requirements come in many levels of detail. The next level after the SOW might be high-level project objectives, science requirements, operational requirements, and so on, descending in ever-increasing levels of detail until finally arriving at the software implementation requirements contained in the SDD.

Lower levels of requirements are derived from the requirements above them, in a top-down fashion. At each level more details emerge and are incorporated into the requirements set in a process known as requirements decomposition, which is a part of the requirements analysis activity. How much time and effort one spends doing requirements decomposition depends on the type of project; some projects are simple enough that a basic set of testable functional requirements will suffice, while others (like the full-authority digital engine controls on jet aircraft, or the guidance and propulsion control systems on spacecraft) might require extensive requirements analysis and decomposition to ensure that all the relevant requirements have been captured, all the off-nominal conditions have been accounted for, and all the low-level implementation requirements necessary to build and program the system are defined and reviewed. The requirements documents for these types of projects can easily run to hundreds of pages. One of the trickier parts of the requirements analysis activity is knowing when enough is enough, and when to keep going to fill in necessary details.

Why Requirements ...