Development of a Simulator for Social Scientific Agent Based Model Kazunari Ishida Faculty of International Agriculture and Food Studies Tokyo University of Agriculture
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Toshizumi Ohta Graduate School of Information Systems University of Electro-Communications
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Abstract We developed a simulator called the Decision-Space-Explorer for developing Socio-Informatica, a modeling platform integrating social scientific papers with the agent-based models they explain. This integration will allow people to interactively share and use knowledge concerning social science with agent-based models. However, the ordinary agent-based model has two problems that make it difficult to use, i.e. employing general purpose language such as Java or Objective-C and deploying a 2 dimensional model framework in every model. To overcome these difficulties in using ordinary agent-based models, we invented a new modeling approach, i.e. decision-making oriented programming and implemented it into the Decision-Space-Explorer with XML technology. Due to the new modeling approach and the implementation, we can now easily develop agent-based models and construct Socio-Informatica. We provide an example and rough evaluations using the simulator for agent-based model to demonstrate its characteristics.
Introduction We developed the Decision-Space-Explorer, a simulation engine of Socio-Informatica, which is a modeling platform that realizes seamless integration between a social simulation model and its paper. The technology of Socio-Informatica is useful for the development of a modeling platform of social informatics [2], because the technology enables the modeling platform of social informatics to become dynamic and interactive media. When many people use Socio-Informatica as a common platform to access knowledge of social informatics, we can explore and exploit the knowledge to sustain our world. To integrate them, we employed agent-based modeling (ABM) and extensible markup language (XML) formalism to describe a social model, because ABM can straightforwardly describe a focused phenomenon with the agents’ decision rule and their interactions, and XML can be a common formalism to define the structure of a document. Moreover, the freely available XML editor can be used to describe a social model because we employ the formalism for our simulator (Fig. 1).
Figure 1: Socio-Informatica and Decision-Space-Explorer
Problems of Ordinary ABM Simulators There are two problems concerning ordinary ABM simulators, e.g. Swarm, RePast, Ascape, and KK-MAS. One is employing a general purpose language. The other is deploying a lattice world framework of the simulators. Ordinary ABM simulators employ a general purpose language, e.g. Java, C++, Objective-C, or dialect of Visual Basic. Because of the ability of the languages, these simulators deal with any model type. However, these languages require that the model builder be a specialist in one of these languages, even though he or she is not trying to develop a complex information system, e.g. operating system, database system, web server and so forth.. The ordinary simulators provide a framework for describing a model world in terms of a 2 dimensional plane or higher dimensional space, i.e. lattice world. The framework enables a model builder to easily describe a model of the food-seeking behavior of ants because they are on the ground. However, if a model builder tries to explore a virtual community, which has no restriction of time, distance, and chance due to the Internet, the lattice framework is not suitable for describing the community, because there are network styled relations between agents in a virtual community.
Social Phenomena in an Information Space Consumer to consumer (C2C) online transactions on eBay and Yahoo Japan auction are examples of newly emerged social phenomena in virtual communities on the Internet. Before the Internet age, C2C transactions were handled at regional markets with respect to fish, vegetables, used goods and so forth. This is because buyers and sellers must meet face to face and talk with each other simultaneously to decide which item should be bought and to find which buyer can buy an item at a high price. Such a transaction used to always be restricted by limitations of time, distance and chance. They were like fixed people on a 2 dimensional lattice ((a) in Fig. 2).
Figure 2: Traditional Society and Information Society
With the advent of the Internet age, they are now able to make deals with all people on the Internet, although they live in different countries. They are not restricted by time, distance and chance, although they have different characteristics ((b) in Fig. 2). The style of interaction among them has become a network style relation instead of a lattice style. In such a social situation, many social phenomena exist. Therefore, many researchers have begun to analyze the phenomena in the social science field.
Primary Elements for Information Society Model What are the fundamental elements to illustrate social phenomena on the Internet? Based on the discussion in the
previous section, we define them in terms of conceptual and technical levels. The conceptual elements are decision-making rules of agents and their network styled interactions. For example, on a C2C online transaction, buyers and sellers select the best people to make deals based on their own decision-making, then they interact with each other to exchange items and money ((a) in Fig. 3).The technical elements are bit strings to express agent characteristics and their operation functions. For example, characteristics of items, which sellers can sell, and those of wants, which buyers want to buy, should be described using various aspects of these characteristics. The representation by a bit string is one of the handy ways to express the characteristics of something in a model, e.g. goods of sellers and wants of buyers ((b) in Fig. 3). The functions to operate bit strings can be useful to handle the strings in a model world.
Figure 3: Fundamental Elements for Information Society Model
Decision-Making Oriented Programming and Simulator Based on the conceptual and technical elements in the previous section, we define a new programming approach, i.e. decision-making oriented programming. To create easier-to-use development tools for agent-based models, we developed a simulation engine for Socio-Informatica. Its modeling language is accurate in describing an agent’s decision-making processes because it employs an IF-THEN style modeling language (Fig. 4). The simulator enables us to describe complex models within a decision-making space easily, and its simple modeling language structure (i.e. IF-THEN) makes it possible to easily equip it with a GUI. Because of the ease with which it allows multi-agent models to be modeled and combined with academic papers, Socio-Informatica is a promising candidate for a de facto standard for modeling agent-based models and publishing papers.
Figure 4: Structure of modeling language in DMO programming
Examples In this section, we will outline the available decision-making oriented programming approaches with a C2C online
market, where each player can simultaneously be a buyer who can supply an item and a seller who has a demand (Fig. 6). They select others to make deals based on reputation, which is a history of transactions, where a buyer always pays money to a seller and a seller always sends the item to a buyer. This is because a player who participates in a C2C online transaction always has the incentive for non-cooperation (i.e., to cheat others), due to anonymity and the ease of entering and exiting from the transaction. On the one hand, a buyer may accept goods from a seller without delivering payment and on the other, a seller may accept payment from a buyer without delivering goods. Hence, they use reputation information derived from histories to decide a buyer or a seller to make the deal. Transaction on an online market is composed of (1) placing items by sellers, (2) seeking possible sellers by buyers, (3) bidding to the best seller, (4) awarding to the best buyer and (5) making the deal as shown in Fig. 5.
Figure 5: C2C Online Transaction
Advantage of DMO Programming and DMO Simulator Characteristics of DMO programming is a modeling approach of an ABM in terms of the decision-making rules of agents and bit string operation functions. The Decision Space Explorer (DSE) is a DMO simulator that is an implementation of DMO programming methodology. DSE expresses simple IF-THEN style rules of agents to describe the decision-making rules of agents. DSE has many bit string operation functions to handle agents’ and the others’ characteristics in a model world. DMO language is defined by the data type definition (DTD) of XML. Because of the employment of XML technology, we can use the freely available XML editors for describing a model instead of ordinary text editors. Due to the simple language structure and employment of the XML editor as GUI for modeling, a model builder can easily describe a model.
References [1]
KK-MAS (Kozo-Keikaku Multi-Agent Simulator), http://www2.kke.co.jp/mas/MASCommunity1.html.
[2]
Ohta, T., K. Ishida, I. Okada, and H. Yamamoto, “Modeling Platform for Social Informatics,” in Proc.s of the 7th International Conference on Systemics, Cybernetics, and Informatics, Orlando, Florida, USA, July 27-30, 2003, Vol. I, pp. 48-53.
[3]
RePast Documentations by the University of Chicago's Social Science Research Computing, http://repast.sourceforge.net/.
[4]
Swarm Development Group’s Documentation, http://www.swarm.org/release-docs.html
[5]
Yamamoto, H., Ishida, K and Ohta, T., “Managing Online Trade by Reputation Circulation: An Agent-Based Approach to the C2C Market,” Proc. of The 7th World Multi-Conference on Systemics, Cybernetics and Informatics, vol. 1, pp.60-64, 2003.
