Michele Marchesi

Software development: do good manners matter?

The research presented in this paper was partly funded by the Engineering and Physical nSciences Research Council (EPSRC) of the UK under grant ref: EP/M024083/1.

Self-organization and market crashes

This paper presents a model of stock price behavior that encompasses both short-term fluctuations and long-term exponential trends punctuated by crashes. The model represents stock market behavior as the interaction of two self-organizing processes. The first process represents business-as-usual stock price fluctuations. It builds on a model of stock price behavior introduced by Cont and Bouchaud. The second process is a risk process that determines the severity of crashes. It is a random graph process driven by macroeconomic variables. Our model is based on the assumption that stock market prices that grow at a higher rate than the real economy force structural changes that, in turn, leverage the risk of a crash. The transition from a business-as-usual regime to a crash regime is determined by trigger events. Trigger events are exponentially distributed while the size of a crash depends on the state of the underlying risk process. While in the short-term the performance of stock prices may be determined by the purely speculative behavior of agents, the long-term behavior of stock prices is essentially a function of structural and macroeconomic parameters.

Studying Lean-Kanban Approach Using Software Process Simulation

We developed an event-driven simulator of the Kanban process a WIP limited pull system visualized by the Kanban board. WIP (work in process) represent the capacity in the activity to perform features simoultaneously. The simulator is fully object-oriented, and its design model reflects the objects of the Lean software development domain. We used this simulator to assess comparatively WIP-limited and unlimited processes. We also studied the optimum values of the working item limits in the activities, using a paradigmatic case of 4 activities and 100 work items. The cost function used is equal to the total time needed to complete the project, plus a weighted sum of the limits themselves. We performed an exhaustive search on all the admissible values of the solution, finding sensible optimal values, and a non-trivial behavior of the cost function in the optimization space.

Software Startups - A Research Agenda

Software startup companies develop innovative, software-intensive products within limited timeframes and with few resources, searching for sustainable and scalable business models. Software startup ...

Simulation of software maintenance process, with and without a work-in-process limit

A software maintenance process is important for reducing maintenance effort and for improving software quality. In recent years, the Lean–Kanban approach has been widely applied in software practice including software maintenance. This approach minimizes Work‐in‐Progress (WIP), which is the number of items that are worked on by the team at any given time, thus improving the maintenance process. In this paper, we describe our simulation studies, which show that the Lean–Kanban approach can indeed help reduce the average time needed to complete maintenance requests. We develop a process simulator that can simulate both existing maintenance processes that do not use a WIP limit and that adopt it. We perform two case studies using real maintenance data collected from a Microsoft project and from a Chinese software firm. The main results of our study are twofold. First, we demonstrate that it is possible to effectively model and simulate, using actors and events, a maintenance process where a flow of issues is processed through a sequence of activities, correctly reproducing key statistics of real data. Second, our results confirm that the WIP‐limited process could be useful to increase the efficiency of software maintenance, as reported in previous industrial practices. Copyright

Simulating Kanban and Scrum vs. Waterfall with System Dynamics

Nowadays, Scrum is the most used Agile Methodology, while the Lean-Kanban approach is perhaps the fastest growing AM. On the other hand, traditional, waterfall-like approaches are still very used in real-life software projects, due to the ease of up-front planning and budgeting, that however are seldom matched upon project completion. In our opinion, more effort is needed to study and model the inner structure and behavior of these approaches, highlighting positive and negative feedback loops that are strategic to understand their features, and to decide on their adoption. In this paper we analyze the dynamic behavior of the adoption of Kanban and Scrum, versus a traditional software development process such as the Waterfall approach. We use a system dynamics model, based on the relationships between system variables, to assess the relative benefits of the studied approaches. The model is simulated using a commercial tool. The proposed model visualizes the relationships among these software development processes, and can be used to study their relative advantages and disadvantages.

Simulation of Software Maintenance Process, with and without a Work-In-Process Limit

A software maintenance process is important for reducing maintenance effort and for improving software quality. In recent years, the Lean–Kanban approach has been widely applied in software practice including software maintenance. This approach minimizes Work‐in‐Progress (WIP), which is the number of items that are worked on by the team at any given time, thus improving the maintenance process. In this paper, we describe our simulation studies, which show that the Lean–Kanban approach can indeed help reduce the average time needed to complete maintenance requests. We develop a process simulator that can simulate both existing maintenance processes that do not use a WIP limit and that adopt it. We perform two case studies using real maintenance data collected from a Microsoft project and from a Chinese software firm. The main results of our study are twofold. First, we demonstrate that it is possible to effectively model and simulate, using actors and events, a maintenance process where a flow of issues is processed through a sequence of activities, correctly reproducing key statistics of real data. Second, our results confirm that the WIP‐limited process could be useful to increase the efficiency of software maintenance, as reported in previous industrial practices. Copyright

Study of the Evolution of an Agile Project Featuring a Web Application Using Software Metrics

We present an agile process used for the development of a Web application written in Java, devised by choosing a set of proven agile practices taken by existing popular agile methodologies. During the project, we regularly measured the software using Chidamber and Kemerer object-oriented metrics suite, and other metrics. The application development evolved through phases, characterized by a different level of adoption of some key agile practices --- such as pair programming, test-based development and refactoring. The evolution of the OO metrics of the system, and their behavior related to the agile practices adoption level is presented and discussed, showing that soft ware quality, as measured using standard OO metrics, looks directly related to agile practices adoption.

Study of the Competition between Proprietary Software Firms and Free/Libre Open Source Software Firms Using a Simulation Model

In recent years, a very important structural change in the software industry took place, with an increasing number of firms that got involved in Free/Libre Open Source Software (FLOSS) development communities. FLOSS communities and products have been studied as complementary to proprietary software companies and products. In this paper we propone a business model for the software market, and in particular we analyze the competition between proprietary software firms and FLOSS firms. Our software market is a system where each agent is independent of each other in the choice about buying or selling software products or services. The proposed work aims to analyze the influence of FLOSS firms producing both software and services in vertical software markets, nowadays mostly dominated by large proprietary firms. The findings show that FLOSS firms are able to compete with proprietary firms, though in the end a monopoly or oligopoly of the latters emerges. The ousted FLOSS firms, however, survive longer than proprietary ones, when these are not able to compete in the market.

Study of the electrical field inside biological structures.

A method to compute accurately the electric field behaviour inside spherical and cylindrical structures is presented. These structures model a living cell and a nerve axon, respectively, taking into account the non-linear electric properties of the lipidic bi-layer surrounding membrane. It is shown that, for most of the cases of practical interest, the linearisation of the membrane characteristic is correct, since the threshold for non-linear effects is very high. When large-size biological structures, such as squid giant axons, are considered, non-linear effects also arise in the case of relatively small applied fields.