The development of large software systems using systems dynamics languages has been hampered by the lack of application of, and support for, modern software techniques. Support is needed to handle the challenges of modular system dynamics model development. These development challenges include the handling of namespaces, linking separate modes, and maintaining clean logical separations among components. Most modern software patterns and languages support such a capability. This paper presents an approach to group, large scale, system dynamics model development that has proven valuable in our project. Our approach included the creation of a software tool, called Conductor, to facilitate our group development. The tool, Conductor, is generally applicable to other projects using Vensim®.
Mental models are bases to recognise phenomena and make plans to improve situations. They can be expressed in model builders' natural language. It is also necessary to examine mental models using a computer simulation. The Computer simulation requires expressions, which can be translated into computer codes. Therefore, model builders need to translate their model from their own natural language to simulation-friendly language, i.e. stock flow diagrams in System Dynamics. It is widely recognised that this translation is sometimes difficult not only for people who are beginners of System Dynamics but also for people who are experienced in the field. This paper discusses a possible translation procedure and shows an application of it. The proposed procedure is designed to use a subset of a natural language as an intermediate language. This idea is applicable regardless of variety of natural language.
Today software vendors have various ways to handle their products. In contrast to non-software products, software products' properties can be changed or controlled at a low cost; vendors do not need to extend their operations, and well-designed software can be customized systematically. Moreover, its diffusion is influenced by network externalities. The diffusion structures of software that have single user type, e.g. World Wide Web browsers, can be expressed mainly as a single reinforcing loop. This is because users can be considered as homogeneous. However, there are multiple possibilities of structure, which corresponds to business strategies for software which has divided users. An example in this category would be highly specialized software, e.g. simulation software. We attempt to explain diffusion processes and characteristics concerning network externalities of software in this category using System Dynamics models. This paper shows that multiple editions can more effectively assist diffusion of main products than strengthening network externality effects.
We describe an attempt to model an enterprises expansion into business adjacencies within the scope of a Master thesis. It was crucial to define a strategy that would allow the Master student to grow with the task (gain experience with modeling), at the same time ensuring communication with the client and proving the ability of qualitative SD modeling to deliver insights.
After identifying problem symptoms, the enterprise problem was explored with methods from Chris Zook: Beyond the Core. Six cases from Zooks book offering points of entry for the enterprise problem were cast into generic archetypes and presented to the problem owner. Two archetypes belonging to the Underachievement class were identified as most relevant for the enterprise problem, viz. 1) underachievement due to long distance between the core and the adjacency, and 2) underachievement due to poor adjacency repeatability. We developed a preliminary system dynamics model embedding both archetypes. The model gives sensible results with basic policies affecting distance to the core and repeatability. The preliminary results have strengthened the clients interest in the modeling work. Further joint modeling sessions have been scheduled. Work is still in progress.
Though evaluation of public policy and projects of government-to-government assistance are quite common in Japan, evaluator use logical model bases for evaluation that is simple tree type model without incorporate loop or feed back effects. Author has insisting that SD modeling is applicable for quantitative evaluation of public policy but find some difficulty with traditional group model building method. In this paper, we wish to discuss new style SD/ST model building for public policy evaluation.
Pressures from human induced climate-change, pollution, and fossil fuel scarcity stimulate interest in alternative fuel vehicles, and in particular hydrogen fuel cell vehicles (HFCVs). The transition from internal combustion engine vehicles to HFCVs is complex as various chicken-egg mechanisms interact in a highly integrated fashion, and the mechanisms are highly non-linear. This paper focuses on one of the most critical chicken-egg problems: the mutualistic dynamics of HFCV adoption and its fueling infrastructure. The effects of local demand-supply interactions on these dynamics are explored in depth. This paper develops a dynamic, behavioral model of vehicle adoption and fueling infrastructure with explicit spatial structure. Simulations are performed for a reduced version. A homogeneous market with strategically locating fuel-station entrants yields fast transition through the formation of adoption clusters (niches). However, under heterogeneous conditions the same micro-mechanisms can counteract the emergence of a sustainable market. Policy implications are significant. This spatial behavioral dynamic model (SBDM) can be used to compare targeted entrance strategies for hydrogen fuel supply. Insights can be used for an aggregate HFCV transition model that includes other mechanisms. Finally, the paper should stimulate a discussion on merits and limitations of spatial modeling as applied to more general socio-economic issues.
This paper discusses a model developed to assess the effects of land-use changes on traffic congestion and air quality. The inputs are characteristics of development and the outputs are time in traffic per capita, and tons of carbon monoxide from vehicles. As previously developed urban dynamics models have done, the model includes a relationship between the output variables and the attractiveness of the area as a place to live. Particular attention is paid in this paper to challenges associated with modeling the relationship between population and land development in urban areas where alternative land-uses are being contemplated. The evolution of an approach to overcoming the challenges is presented.
This paper uses the framework proposed by Rouwette et al. (2002) to describe the group model building stage of a project to integrate land use, transportation and air quality planning in a rapidly growing metropolitan area. The purpose of the paper is twofold: to present a case of group model building in the public sector, and to test the framework for reporting about group model building interventions. The main goal of the intervention described is to evaluate the effect of potential land use and transportation policy changes on urban quality of life factors such as air quality and traffic congestion. A secondary goal is to foster interagency and intergovernmental collaboration. After approximately 15 months, the project is at the end of its first stage. A quantitative model has been completed and is being tested by the modeling group. In the next stage, the model will be used by policy-makers for policy evaluation.
This article attempts to build a simulation model of the impacts of factors that facilitates faculty adoption of Web-Based Instruction (WBI) from the perspective of the faculty stages of concerns. Faculty have different concerns as they integrate new technology into their teaching. Without reducing these concerns, WBI integration will not be successful. Four main stages of faculty concern (information, personal, management, and impact concern) were identified based on Halls concern-based adoption model. Reviewing literature on the diffusion of on-line education, we have identified support factors that may decrease facultys concerns for adopting WBI in their education settings. These factors were incorporated into the simulation model in order to test the potential impacts of the factors on faculty adoption of WBI. The current simulation model built in Stella® will aid educators or administrators to evaluate the impact of the factors on adoption of WBI.