ANALYSIS OF SOME APPROACHES TO QUANTITATIVE EVALUATION OF SOFTWARE RELIABILITY
The article is the extension of the subject matter of the authors published before. The emphasis is on the construction of quantitative evaluation of software reliability factors (subcharacteristics) such as maturity, fault tolerance, recoverability, availability on the level of proper measures. The corresponding factors are identified in international standards documentations. Substantial analysis of ISO/IEC 25023 approaches to quantitative evaluation of software reliability measures are performed based on peculiar features of special purpose automated systems meant for field use. As for the internal for maturity it is stressed that the ISO/IEC 25023 suggestion is characterized by significant errors in estimating the mean faultless time for software. The main reason is that the intensity of failures is declining as software faults are found and operation time growing. Such the effects must be taken into account. In view of fault tolerance importance for automated systems under consideration it is reasonable to increase the number internal measures including process restoration means for entrance errors, incorrect actions of the operator and so on. As a result some refinements for the choice of measures to estimate software reliability factors as well as for constructing the corresponding methods to calculate quantitative values of measures are proposed. To go into details it is recommended that the maturity internal measure calculation procedure must depend of software faults elimination process. The most promising in this attitude is the approach based on calculation the number of experiments till finding the fault when testing software. The approach is developed by one of the authors of the article.