scm

Software Configuration Management

The most frustrating software problems are often caused by poor configuration management. The problems are frustrating because they take time to fix, they often happen at the worst time, and they are totally unnecessary. For example, a difficult bug that was fixed at great expense suddenly reappears; a developed and tested feature is mysteriously missing; or a fully tested program suddenly doesn't work. Configuration management helps to reduce these problems by coordinating the work products of the many different people who work on a common project. Without such control, their work will often conflict, resulting in such problems as:

Simultaneous Update

When two or more programmers work separately on the same program, the last one to make the changes can easily destroy the other's work.

Shared Code

Often, when a bug is fixed in code shared by several programmers, some of them are not notified.

Common Code

In large systems, when common program functions are modified, all the users need to know. Without effective code management, there is no way to be sure of finding and alerting every user.

Versions

Most large programs are developed in evolutionary releases. With one release in customer use, another in test, and a third in development, bug fixes must be propagated between them. If found by a customer, for example, a bug should be fixed in all later versions. Similarly, if a bug is found in a development release, it should be fixed in all those prior versions that contained it. In larger systems with several simultaneous active releases and many programmers working on bug fixes and enhancements, conflicts and confusion are likely.

These problems stem from confusion and lack of control, and they can waste an enormous amount of time. The key is to have a control system that answers the following questions:

What is my current software configuration?
What is its status?
How do I control changes to my configuration?
How do I inform everyone else of my changes?
What changes have been made to my software?
Do anyone else's changes affect my software?

The key role of Software Configuration Management (SCM) is to control change activity so these questions can be answered. If, however, SCM is viewed merely as a management tool or contractual obligation, it can easily become a bureaucratic roadblock that impedes the work. While such systems may be contractually required, the real need is to assist the programmers in controlling and tracking their work, while ensuring that nothing is lost or destroyed.

-- Watts Humphrey
Managing the Software Process
Addison-Wesley, 1989