6.4. Extension and Reuse of the Reference Simulation Model The SD model developed in the previous section can be extended and reused in several ways. For example, as mentioned earlier, it is possible to make the model more realistic by adding a causal relationship between the number of errors detected and the fraction (size) of the artefact to be reworked. The more interesting aspect of reusability is illustrated by Fig. 12. The figure shows the V-model software development process on the right hand side. Simulation models representing the Design and Coding phases are presented as boxes. For example, the Boxes labelled views C to C represent the SD model views presented in Figs. 7–9. In Figs. 7–9, the code documents developed and verified in the coding phase are represented by one single level variable. There is no differentiation between code subsystems or modules. To facilitate a more detailed representation of reality, i.e., explicit modelling of individual subsystems (or even modules, the SD tool VENSIM ® offers the possibility of “subscripting,” i.e., the possibility of replacing a monolithic entity by an array of entities of the same type. A subscript works like the index of an array. With the help of this mechanism, potentially all variables used in the model views C to C can be duplicated. For example, if five code subsystems shall be modelled, they would be represented by level variables code doc size [1] to code doc size [5], or, if 100 code modules are to be modelled, the index of code doc size would run from 1 to 100, each index representing the levels and rates associated with each module. Requirements Design Code Unit Test System Test Integration Test View 1D View 2D View 3D Subscripting View 1C View 2C View 3C Subscripting V-Model: Development, Verification (Inspection, Validation (Test) Real-World Processes Simulation Model
