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Tuesday, August 4, 2009

Do software systems age analogously to humans?

Having worked in software industries for a long time, this question, posted in an introduction to a paper by the noted and respected Computer Scientist, David Parnas, in a book seems kind of obvious to me and no doubt to many practitioners. However, there are software companies that still hold this belief of "Design once last forever" philosophy and need not change at all. They are also unfortunately pursuers of this illusive Silver Bullet that another noted and respected scientist, Fredrick Brooks, has warned. They naturally do not believe software can age.

Having worked in such a nescient organisation, I am interested to read what Parnas has to say when I come across his paper "Software Aging". There are specifics that I believe worth mentioning here.

One of the good ways to slow down or even to deal with changes, is to design to cater for changes using well-known design principles. In his research and experience, sadly "I do not see much software that is well designed from this point of view" and he gave some of the reasons why:
... The principle is simple; applying it properly requires a lot of thoughts about the application and the environment. The textbooks do not make that clear.

Many programmers are impatient with such considerations; they are so eager to get the first version working or to meet some imminent deadline, that they do not take the time to design for change. Management is so concerned with the next deadline (and so eager to get to a higher position) that future maintenance costs don't have top priority.

Designs that result from a careful application of information hiding are quite different from the "natural" designs that are the result of most programmers' intuitive work.....

Programmers tend to confuse design principles with languages.... Even worse, they think that one has applied the techniques, if one has used such a language. [Sadly, in my professional experience many managers are the big champions of this (mis)belief creating massive software problems and wastes.]

Many people who are doing software development, do not have an education appropriate to the job.
Italics text are my comments.

One of the topic that he commented on that I share passionately that is often not done in Software Industry as compared with others, such as other forms of engineering and medicines is the topic of reviews despite its effectiveness supported by abundance of well publicized materials. Robert Glass even proclaims that it is "being a breakthrough as anything we have". Parnas said
it is quite astonishing to see how often commercial programs are produced without adequate reviews. There are many reasons for this:
  • Many programmers have no professional training in software at all. Some are engineers from other fields; some are "fallen scientists" who learned programming incidentally while getting education... In many of those areas, the concept of preparing and holding a design review is nonexistent.
  • Even among those that have Computer Science degrees many have had an education that neglected such professional concerns as the need for design documentation and reviews....
  • Many practitioners (and many researchers) do not know how to provide readable precise documentation of a design, as distinct from an implementation. No precise description, other than the detailed code, is available for review. Design reviews early in a project, when they would do the most good, are often reduced to chat sessions....
  • Much of software is often produced as a cottage industry, where there are no people who could serve as a qualified reviewers ....
  • Software is often produced under time pressure that misleads the designers into thinking that they have no time for proper reviews.
  • Many programmers regard programming as an "art" and resent the idea that anyone could or should review the work that they have done.
I also share Parnas' concern that "it is common to hear a programmer saying that the code is its own documentation; even highly respected language researchers take this position, arguing that if you use their language, the structure will be explicit and obvious"

My argument with proponent of this view is that code does not document a design; it merely documents an implementation of a design decision. There are plenty of materials a designer has discarded that are vitally important to the maintenance of the implementation but are not and cannot be translated to code. For example, technologies or algorithms that a designer has considered by discarded and for what reasons are not found in code and cannot be for practical reasons. Design decisions why it is done this way and not another are not found in code; in fact, lack of supplemental information that we called documentation one could be misled from reading code. They cannot be deduced from code no matter what language one uses or how clever one uses the language construct to aid documentation.

Parnas went on to say "Even if we take all reasonable preventive measures, and do so religiously, aging is inevitable." and in that paper he offers many practical advices to deal with software aging, including "start taking documentation more seriously".

Daniel M. Hoffman and David M. Weisss, "Software Fundmentals - Collected Papers by David L. Parnas" 2001. Chapter 29 "Software Aging"

Robert L. Glass, "Facts and Fallacies of Software Engineering", page 104

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