Simulating global software evolution processes by combining simple models: an initial study

Abstract

A number of studies of the long-term evolution of commercial software products over many releases have established a consistent pattern for growth in the size of the systems examined. This shows a trend towards a progressive slowdown in growth over time. The work described here forms the first step in developing a simulation of the combined effects of the causes of this trend. A number of simple system dynamics simulations, each capturing the causal structure and behaviour of one of a number of causes believed to contribute to the observed behaviour, and its calibration to follow the observed trend, is presented. These models are then combined into a single simulation model reflecting the effect in combination of these causes. Possible causes considered here are: the reduction over time in both the conceptual space which can be searched for new uses of a system and the design spaces constraining developers' ability to modify their systems, the effects of the degradation of the structure of a software system as is it is evolved in unanticipated directions, and the reducing coverage of developers' knowledge of the structure of the system. The combined model incorporates all of these causal mechanisms and introduces a relative weighting for each. The long-term aim of this work is to produce a simulation embodying those possible causes which are found to be supported by actual evidence. Calibration of this model to reflect the relative importance of each cause in a real-world situation should then enable it to reproduce the actual software system size trend, so assisting in identifying those causes which affect most significantly the growth trend of that system.

Software evolutionary dynamics modelled as the activity of an actor-network

“…The influence of this mindset can be seen, for example, in [5], in which their Figure 1 shows a program surrounded by people, who are interacting with it but which are very obviously different sorts of things from the program itself. This mode of thinking is also implicit in our simulation models, in which we have sought to describe this process [3,16,17,19]. By way of contrast, Latour's actor-network theory (ANT) [7], an approach based on a sociological view of technological change, provides us with a viewpoint from which the effects of both human and technical participants on process characteristics and behaviour can be considered on a more equal footing.…”

A policy investigation model for long-term software evolution processes

“…It is further delayed as completed requirements have to wait until the next release of the software is delivered to its users. The effective effort available is reduced over time by an inertia-like effect (Wernick and Hall, 2002) in a manner related to the size of the existing system (Turski, 2002).…”

“…This is multiplied by a factor reflecting the effects of the existing system size on the ability to evolve it. This results in a reduction of effective throughput over time, due both to the inertia of the existing system and to a reduction in system-wide knowledge (Wernick and Hall, 2002). The overall effect on effort due to system size is calculated as a multiple of the inverse cube (Turski, 2002) of that size.…”

“…• effectiveness of staff working, reflected in the rate of starting work on new enhancements/fixes • speed of development cycle, reflecting for example the ability to speed up the development process from requirements to code ready to ship and/or reduced delays from completion of an enhancement to incorporation in a fielded release • maintainability of the system, represented as the inertia of the existing system making any change more difficult, and reflected to the size of the exiting system (Wernick and Hall, 2002) • effectiveness of the process in correctly identifying requirements and converting these correctly into system functions delivered to users…”

“…The current simulation structure is a simple mathematical representation of a theory (Wernick and Hall, 2002) of this phenomenon. Future research will hopefully identify the causal strucure underlying this representation, and allow a calibration based on real-world metrics rather than the current calibration to fit.…”