To understand the necessity for software engineering, we must pause briefly to look back at the recent history of computing. This history will help us to understand the problems that started to become obvious in the late sixties and early seventies, and the solutions that have led to the creation of the field of software engineering. These problems were referred to by some as “The software Crisis,” so named for the symptoms of the problem. The situation might also been called “The Complexity Barrier,” so named for the primary cause of the problems. Some refer to the software crisis in the past tense. The crisis is far from over, but thanks to the development of many new techniques that are now included under the title of software engineering, we have made and are continuing to make progress.
In the early days of computing the primary concern was with building or acquiring the hardware. Software was almost expected to take care of itself. The consensus held that “hardware” is “hard” to change, while “software” is “soft,” or easy to change. According, most people in the industry carefully planned hardware development but gave considerably less forethought to the software. If the software didn’t work, they believed, it would be easy enough to change it until it did work. In that case, why make the effort to plan?
The cost of software amounted to such a small fraction of the cost of the hardware that no one considered it very important to manage its development. Everyone, however, saw the importance of producing programs that were efficient and ran fast because this saved time on the expensive hardware. People time was assumed to save machine time. Making the people process efficient received little priority.
This approach proved satisfactory in the early days of computing, when the software was simple. However, as computing matured, programs became more complex and projects grew larger whereas programs had since been routinely specified, written, operated, and maintained all by the same person, programs began to be developed by teams of programmers to meet someone else’s expectations.
Individual effort gave way to team effort. Communication and coordination which once went on within the head of one person had to occur between the heads of many persons, making the whole process very much more complicated. As a result, communication, management, planning and documentation became critical.
Consider this analogy: a carpenter might work alone to build a simple house for himself or herself without more than a general concept of a plan. He or she could work things out or make adjustments as the work progressed. That’s how early programs were written. But if the home is more elaborate, or if it is built for someone else, the carpenter has to plan more carefully how the house is to be built. Plans need to be reviewed with the future owner before construction starts. And if the house is to be built by many carpenters, the whole project certainly has to be planned before work starts so that as one carpenter builds one part of the house, another is not building the other side of a different house. Scheduling becomes a key element so that cement contractors pour the basement walls before the carpenters start the framing. As the house becomes more complex and more people’s work has to be coordinated, blueprints and management plans are required.
As programs became more complex, the early methods used to make blueprints (flowcharts) were no longer satisfactory to represent this greater complexity. And thus it became difficult for one person who needed a program written to convey to another person, the programmer, just what was wanted, or for programmers to convey to each other what they were doing. In fact, without better methods of representation it became difficult for even one programmer to keep track of what he or she is doing.
The times required to write programs and their costs began to exceed to all estimates. It was not unusual for systems to cost more than twice what had been estimated and to take weeks, months or years longer than expected to complete. The systems turned over to the client frequently did not work correctly because the money or time had run out before the programs could be made to work as originally intended. Or the program was so complex that every attempt to fix a problem produced more problems than it fixed. As clients finally saw what they were getting, they often changed their minds about what they wanted. At least one very large military software systems project costing several hundred million dollars was abandoned because it could never be made to work properly.