The Limits of Software – Part II- The Problems of Functionality

Consider the requirements for the avionics of a multi-engine aircraft, a cellular phone switching system, or an autonomous robot. The raw functionality of such systems is difficult enough to comprehend, but now add all of the (often implicit) nonfunctional requirements such as usability, survivability, and adaptability, indeed, all of the forces that shape a system. These unrestrained, potentially contradictory, external requirements are what amplify the arbitrary complexity ….
This external complexity usually springs from the “impedance mismatch” that exists between the users of a system and its developers: users generally find it very hard to give precise expression to their needs in a form that developers can understand. In extreme cases, users may have only the vaguest ideas of what they want in a software system.

Moreover, developers may not even know exactly the expectations of its user base, especially in the case of emerging, rapidly changing markets.

This is not so much the fault of either the users or the developers of a system; rather, it occurs because each group generally lacks expertise in the domain of the other. Users and developers have different perspectives on the nature of the problem and make different assumptions regarding the nature of the solution.

Actually, even if users had perfect knowledge of their needs, it is intrinsically difficult to communicate those requirements precisely and efficiently.

At one extreme, the development team may capture requirements in the form of large volumes of text, occasionally accompanied by a few drawings. Such documents are difficult to comprehend, are open to varying interpretations, and too often contain elements that are designs rather than essential requirements.

At the other extreme, there will be no stated requirements, only general visions and some specific stories, all retained in the heads of the developers. This may work for exploratory development or ultra-lightweight projects, but it is absolutely impossible to manage a development process against invisible requirements.

گزیده:

A life without love, is no life at all.
– “Ever After: A Cinderella Story”