Ever-increasing maintenance costs

We like to think that a program, once written, tested, and deployed, is "finished". We like to think that it is a completed work, something we can leave in place and forget about.

But programs are not static elements. The maintenance costs of a given program tend to increase over time.

Now, programs often change over time. Once version 1.0 has been released, we often start working on version 1.1 (or 1.2, or 2.0, depending on one's ideas towards version numbers). Those changes usually increase the size and complexity of the code, which means an increase in maintenance expense. More code costs more to maintain.

Yet even with no changes, maintenance costs increase. At first glance, this seems wrong. Why would cost increase when the code remains unchanged?

Compilers and languages change over time. New versions of compilers implement new versions of languages. Sometimes, these changes cause existing code to break.

A subtler change occurs when new features are added to a language. The C++ language was modified to include the STL. Microsoft modified C# to include the LINC functions. Sun and Oracle have enhanced Java.

While enhancements do not (usually) break existing code, they do change the core knowledge used by programmers. Today, it is a poor C++ programmer who does not use the STL, and a poor C# programmer who avoids LINC. The enhancements become part of the "working set of knowledge".

Yet those old programs, the ones we think are "finished", may be old enough to pre-date the enhancements. When maintained, programmers have to think back to "the old days" and remember the old-fashioned methods for accomplishing certain tasks. A programmer may be able to use the new language features to add functionality to a program, but he must be able to read the old-style code.

When the idioms of old-style code are no longer popular, then fewer programmers understand them. Thus, to successfully maintain an older program, you as project manager must find a programmer who does understand the old-style code, or you must allow a less-experienced programmer time to learn the old idioms. That's the increase to your maintenance costs: more money for a scarce resource, or more time for an available resource.

No program stays "modern", at least not without constant upkeep. We build programs on top of compilers, languages, libraries, operating systems, databases, and communication protocols. All of these "platforms" change, regardless of our business.

The idea that a program is "finished" is a false one. Programs live in an ocean of change, and they must evolve and adapt in that ocean.