SOFTWARE RELIABILITY MODELS COST Prof. Dr. PANAGIOTIS SINIOROS Technological Educational Institute of Piraeus Athens Greece Prof. Dr. ION IVAN, Lect. Dr. MARIAN DÂRDALĂ, Academy of Economic Studies Bucharest ABSTRACT: Software qulity improvment, in the same way, have important results. For software reliability, an important characteristic of software quality, there are lots of models. This paper presents some of the models of reliability cost (linear model, nonlinear model).We estabilshed in a case of falling cost to one percent increase of software reliability. The problem of improvement the cost of reliability is very important for the development of indispensable software in the guiding proceeding of nuclear power station. KEY WORDS: Software Reliability, Cost Model

1. Introduction The development of electrical production in the nuclear power station has low level of cost and pollution like advantage. The reduction of accident risk needs to develop software with high level of reliability. The power nuclear stations have special managerial conditions (the correlations between consumption and production, quality and structure of proccess). The development of reliability software is possible using a modern technologies (structured analysis, object oriented analysis, Jackson system development, data flow oriented design). The succes of technologies depends of CASE (Computer Aided Software Engineering) used. The software reliability means a complexity and dimensin increased. The software for nuclear power station particularry must have the greatest reliability. Such a software becomes useless because of its speed decrease while its cost an exponential increase.

2. The models of software reliability cost There are created models for different steps of the software development cycle. The models quality depends the follows: Work hypotesis Factor numbers Estimation methods Stock of programs 2.1. The estimated cost Considering set of programs {P1, P2, P3, …, Pn} extant, their complexity and expanses are measured. The model is: Ce=a*ebk, where Ce – estimated cost, k – program complexity, a,b – coefficients. The a, b coefficients are estimated using the least squares method with data series having n terms. If we associate for a programm a tree structure of modules and complexity level is measured for each of module (Mi), the estimated cost is: m

Ce ai ebi k i A * m where:

i 1

ki – the complexity level of module (Mi) m – number of modules A - assembly cost

ai, bi – the estimated coefficients We can create complexity classes using the decomposed in modules. We estimated the ai,bi coefficients for each complexity class and we create a table with this coefficients. 2.1. The project cost This model contains the express computed during the proccess The model structure: m

c p chq (chpi chd i chti chai ) ci ch ct cw ca cl cc where:

i 1

m – number of models chq – project expenses chpi – expenses for the i modul programming chdi – expenses for created of a test example of the i modul chti – expenses for i modul testing chai – expenses for the i modul assembly ci – expenses for interface construction ch – self documentation expenses ct – expenses for global testing cw – expenses for performed training cc – expenses for computer use ca – archive expenses cr – reproduction expenses 2.1. The effective cost This cost is resulted from accounting: p

p

Cf cij , i, j 1.. p i 1 i 1

where:

Cf – effective cost P – stage number of software development cycle Cij – expense that was done in the i-th stages for the j-th stages. This cost have to be corelated each other. The first cost create an image about the resources level. The second cost mobillize resource. The third cost account the effective consumptions.

3. Reliability cost The software reliability cost is part of effective cost and project cost and estimated cost. It’s very important to establish the reliability cost weight in total cost. We define the methods for separate expenses on quality characteristic. The reliability cost is computed like software complexity variation.

cf ccc( 1 2 3 4 ) where:

cf – software reliability cost ccc – overagecost of quality characteristic

i

- the unrealization of a characteristic in composes with a normated level (

- mentenability,

3 - portability, 4

1 - corectness, 2

- reliability)

4. Conclusion This theoretical results will be experimented in the future for create reliability software to help management in the nuclear power stations.

5. Acknowledgements This paper continues our research activity. The work group encourage by T.E.I., A.S.E., I.C.I, National Commision for Research and High Education System Department.

Reference

1. J.C. Bolot – Cost – quality tradeoffs on the Internet, Computer Networks and ISDN Systems, vol. 28 nr. 5, 1996, pp. 645-652 2. B. Henderson-Sellers – Object-Oriented Metrics Measures of Complexity, Prentice Hall PTR Upper Saddle River, New Jersey, 1996 3. M. Shepperd – Foundation of software measurement, Prentice Hall, London 1995 4. C.W. Krueger – Software Reuse, ACM Computer Surveys, pp. 131 –184, vol 24, nr 2, 1992.

1. Introduction The development of electrical production in the nuclear power station has low level of cost and pollution like advantage. The reduction of accident risk needs to develop software with high level of reliability. The power nuclear stations have special managerial conditions (the correlations between consumption and production, quality and structure of proccess). The development of reliability software is possible using a modern technologies (structured analysis, object oriented analysis, Jackson system development, data flow oriented design). The succes of technologies depends of CASE (Computer Aided Software Engineering) used. The software reliability means a complexity and dimensin increased. The software for nuclear power station particularry must have the greatest reliability. Such a software becomes useless because of its speed decrease while its cost an exponential increase.

2. The models of software reliability cost There are created models for different steps of the software development cycle. The models quality depends the follows: Work hypotesis Factor numbers Estimation methods Stock of programs 2.1. The estimated cost Considering set of programs {P1, P2, P3, …, Pn} extant, their complexity and expanses are measured. The model is: Ce=a*ebk, where Ce – estimated cost, k – program complexity, a,b – coefficients. The a, b coefficients are estimated using the least squares method with data series having n terms. If we associate for a programm a tree structure of modules and complexity level is measured for each of module (Mi), the estimated cost is: m

Ce ai ebi k i A * m where:

i 1

ki – the complexity level of module (Mi) m – number of modules A - assembly cost

ai, bi – the estimated coefficients We can create complexity classes using the decomposed in modules. We estimated the ai,bi coefficients for each complexity class and we create a table with this coefficients. 2.1. The project cost This model contains the express computed during the proccess The model structure: m

c p chq (chpi chd i chti chai ) ci ch ct cw ca cl cc where:

i 1

m – number of models chq – project expenses chpi – expenses for the i modul programming chdi – expenses for created of a test example of the i modul chti – expenses for i modul testing chai – expenses for the i modul assembly ci – expenses for interface construction ch – self documentation expenses ct – expenses for global testing cw – expenses for performed training cc – expenses for computer use ca – archive expenses cr – reproduction expenses 2.1. The effective cost This cost is resulted from accounting: p

p

Cf cij , i, j 1.. p i 1 i 1

where:

Cf – effective cost P – stage number of software development cycle Cij – expense that was done in the i-th stages for the j-th stages. This cost have to be corelated each other. The first cost create an image about the resources level. The second cost mobillize resource. The third cost account the effective consumptions.

3. Reliability cost The software reliability cost is part of effective cost and project cost and estimated cost. It’s very important to establish the reliability cost weight in total cost. We define the methods for separate expenses on quality characteristic. The reliability cost is computed like software complexity variation.

cf ccc( 1 2 3 4 ) where:

cf – software reliability cost ccc – overagecost of quality characteristic

i

- the unrealization of a characteristic in composes with a normated level (

- mentenability,

3 - portability, 4

1 - corectness, 2

- reliability)

4. Conclusion This theoretical results will be experimented in the future for create reliability software to help management in the nuclear power stations.

5. Acknowledgements This paper continues our research activity. The work group encourage by T.E.I., A.S.E., I.C.I, National Commision for Research and High Education System Department.

Reference

1. J.C. Bolot – Cost – quality tradeoffs on the Internet, Computer Networks and ISDN Systems, vol. 28 nr. 5, 1996, pp. 645-652 2. B. Henderson-Sellers – Object-Oriented Metrics Measures of Complexity, Prentice Hall PTR Upper Saddle River, New Jersey, 1996 3. M. Shepperd – Foundation of software measurement, Prentice Hall, London 1995 4. C.W. Krueger – Software Reuse, ACM Computer Surveys, pp. 131 –184, vol 24, nr 2, 1992.