Shih-Kung Lai

Decision Network: A Planning Tool for Making Multiple, Linked Decisions

Few techniques exist specifically for planning analysis. Commonly used decision techniques focus on different, partial aspects of coordinating decisions. The garbage-can model focuses on the context in which decisions emerge to explain descriptively how organizational choices are made; the strategic choice approach focuses on the relationship between decisions from which rational actions can be taken; and the decision tree focuses on the causal sequence of decisions from which the optimal path of a plan can be derived. Drawing on the theoretical foundation of these three commonly used techniques, we introduce the conceptual framework of a tool for planning analysis, namely Decision Network, that addresses context, relationship, and sequence of decisions, with a numerical example demonstrating how the decision problem can be formulated and solved. Decision Network can be used by decision makers who are faced with more than one decision in order to make plans. Much can be built on this tool to address spatial issues.

Effects of Planning on the Garbage-Can Decision Processes: A Reformulation and Extension

A computer simulation, based on the garbage-can decisionmaking process, is presented in order to investigate effects of making plans and of two other organizational characteristics—namely, decision cost and problem disutility—on the behavior of complex systems. In this simulation a three-factor factorial design was implemented where decision cost, problem disutility, and planning investment were considered in terms of combinations of six levels of these factors. The results suggest that all three factors have statistically significant effects on the behavior of the complex system. In particular, decision cost and problem disutility tended to have effects counter to each other, whereas planning resulted in more efficient decisionmaking, but at the cost of resolving fewer problems.

A Spatial Garbage-Can Model

In this simulation, based on a spatial garbage-can model, I treat the urban dynamic system as a set of random-walk elements interacting with each other in time. Five elements are considered: decisionmakers, choice opportunities, problems, solutions, and locations. Decisionmakers, problems, and solutions meet in an unpredictable way, are thrown into garbage cans as choice opportunities in certain locations, and something happens. In contrast to most traditional spatial simulation techniques, in which space is global and static, I consider in this simulation locations of facilities as dynamically floating on the stream of opportunities, interacting with other elements. The simulation results imply that the relationship between problems and choice opportunities dominates the outcome of the evolution, whereas the effects of the spatial structure as well as the structures of decision and solution are insignificant. The model may provide useful insights into how urban dynamics evolve.

Are cities dissipative structures

The new emergent paradigm of urban development theory that is based on complexity sciences allows us to understand and analyse cities in a new way. Theoretically, complexity sciences enable us to depict the fundamental characteristics of urban development, including nonlinearity, self-organization, and emergence. Empirically, the agent-based modelling (ABM) approach can help us to conduct simulations of complex systems, including cities, in an effective way. In the present paper, we demonstrate a computer simulation of urban growth based on the spatial garbage can model represented in an ABM framework. In the simulation, we treated the city as an open system in that the fundamental elements of the system flow in and out of the system over time. We then computed over time the levels of entropy as a measurement of the degree of structural order of the systems, namely, decision and spatial structures. The results showed that these entropies decreased over time, indicating that the city self-organizes itself reminiscent of a dissipative structure.