Stepwise approach for introducing object-oriented technique at software maintenance stages

Software maintenance, including improvement and conversion, is becoming essential. It is repeated many times for the survival of software, but its cost is quite expensive. Though it is said that the object-oriented technique is effective to lower the cost of software maintenance, in applying the object-oriented technique to the existing conventional software, many problems are reported such as time-consuming reeducation of software developers, large cost, or not so remarkable instantaneous effect. This paper discusses a methodology to apply the object-oriented technique to software already developed by conventional techniques at its maintenance stages. In order to settle the above-mentioned problems and easily realize the introduction of the object-oriented technique at its maintenance stages, we propose a step-wise approach dividing the process of applying the object-oriented technique into 4 phases. The first and second phases of this methodology were applied to a part (about 1/3 namely around 50 kilo-steps in C/C++ language) of a large-scale practical system for scheduling elevator maintenance engineers. The result showed the above expectation was true and the object-oriented technique must lower the cost of software maintenance since the number of bugs in the applied part was about one tenth of that of the unapplied part