The benefit of low-cost labor must be weighed against the risk of missed deadlines, dissatisfied users, and failure to reduce development costs.

No abstract

Studies show that the maintenance stage of the software life cycle consumes a farge proportion of software development resources. They also show that the maintenance cost of a software product hreases with age and that it costs less to maintain the redeveloped software product. Thus, it may be worthwhile to redevelop software to reduce the maintenance costs but the redevelopment costs may prohibit thii. This paper discusses the nature and behaviour of software maintenance costs and sdtware development costs. In order to minimize the sum of maintenance and development costs for a software product, it recommends and illustrates the use of replacement theory. The replacement model suggested in thii paper will be useful for choosing between redeveloping the software and maintaining the existing sofhare. This paper provides a worked example consistent with replacement theory. Since capital is in short supply, replacement projects have to vie with new software and maintenance projects for funding. This paper also describes building a software project portfolio of new software development, software maintenance, and software redevelopment projects. 14, 103-109. 21, 61-67. of Information Systems, Gray, P. et al. (eds) Dryden Press, Chicago, IL, pp. 231-244. Journal of Software Maintenance, 2, 157-174.

No abstract

The process of constructing a correct simulation model for a system is a difficult and time-consuming task in the simulation life-cycle. Simulation is a widely used methodology for checking the performance requirements of information systems. This paper describes a knowledge-based approach to constructing a simulation model of an information system. The approach consists of two major steps: first, the information system is modeled as a Petri Net and implemented in a logic-based language. Second, the executable representation of the Petri Net is used to automatically construct a simulation model of the information system in GPSS. The approach offers several benefits such as reducing system development time, allowing the flexibility of easy modifications to the information system configuration, and requiring little knowledge of simulation methodology. The knowledge-based system is implemented in PROLOG.