Foundations of Management, Vol. 9 (2017), ISSN 2080-7279 DOI: 10.1515/fman-2017-0022 287 WEB-BASED TOOLS FOR SYSTEM DYNAMICS SIMULATION Małgorzata ŁATUSZYŃSKA University of Szczecin, Faculty of Economics and Management, Szczecin, Poland e-mail: [email protected] Abstract: A rapid development and omnipresence of the World-Wide-Web and its technologies have had remarkable impact on the field of computer simulation, understood as a numerical technique for conducting experiments with certain types of mathematical and logical models, describing the be- havior of a system on a computer over extended periods of time. One of the computer simulation meth- ods used to solve complex management problems is System Dynamics (SD). The aim of this paper is the review of SD Web-based tools in the context of some technology aspects of Web-based simulation and its advantages and disadvantages. Keywords: System Dynamics, Web-based simulation 1 Introduction Although the notion of Web-based simulation is probably as old as the Web itself (Reichenthal, The Internet and its multimedia front-end, the 2002), early WBS efforts began in 1995, first World-Wide-Web (WWW), has experienced re- by providing Web-front ends to simulations running markable growth since its introduction by Berners- as Common Gateway Interface (CGI) scripts Lee in 1989 (CERN, 2017). Many disciplines have /programs. In addition, work began on Java-based re-evaluated their strategies, methods and techniques simulation packages, systems and environments that in the view of services offered by the Internet (Byrne would run anywhere on the Web. Results from these et al., 2010). A rapid development and ubiquity activities were first reported in the Winter Simula- of the WWW and its technologies have had also tion Conference in 1996 (Buss and Stork, 1996; an impact on the field of computer simulation, un- Fishwick, 1996; Kuljis, 1996; Nair and Miller, derstood as a numerical technique for conducting 1996). From this event, the interest and level of re- experiments with certain types of mathematical search effort in the area of Web-based simulation and logical models describing the behavior of a sys- grew continuously, which is reflected by an increas- tem on a computer over extended periods of time ing number of publications on this subject. Fig. 1 (Naylor et al., 1967). Kuljis and Paul (2001) go so presents an upward trend of scientific works relating far as to state that the pressure imposed by the in- to Web-based simulation, published in ScienceDi- crease of the Web uses has forced the simulation rect, in the decade of 1996−2015. community to migrate to the Web in order to stay Most papers appeared in “Simulation Modelling “alive”. Practice and Theory”. The reviewed papers dis- A Web-based simulation (WBS) can be defined as cussed both the technical aspects of the Web-based the use of resources and technologies offered by the simulation and its tools (Discrete Event Simulation, Internet for ensuring an interaction with the client Multi-Agent Simulation or System Dynamics Simu- and server modelling and simulation tools (Byrne et lation) as well as its application in various fields, al., 2010; Kuljis and Paul, 2001; Maciąg et al., such as medicine, education, computer games 2013). A common characteristic of all WBS applica- or decision support systems. tions is that they use a Web browser as a support The aim of this paper is the review of System Dy- for graphical interfaces connecting the user with namics (SD) Web-based tools in the context of some simulation. technology aspects of Web-based simulation and the advantages and disadvantages of WBS. 288 Małgorzata Łatuszyńska 25 20 15 10 5 0 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Number of publications Trend Figure 1. Number of publications relating to WBS in 1996−2015 (source: own study) 2 Categories and technologies of Web-based Fig. 2 presents the basic local S&V configuration, simulation after the initial loading phase. During this loading phase, the user opens a browser and navigates to a Web page typically containing an applet, and Relevant research suggests several categories of Web the browser automatically calls for the applet that -based simulation, depending on the adopted criteria is seamlessly downloaded to the client’s computer. (for example, see Bencomo, 2004; Myers, 2004; In this case, the applet contains both the simulation Page, 1999; Whitman et al., 1998). This paper focus- engine and the visualization/animation engine, which es on the types related to descriptions of how WBS execute locally on the client-side. There may be applications can be developed architecturally, that is: a more advanced configuration in which, for exam- ple, a database might be present on the server-side local simulation and visualization, (Byrne et al., 2010). remote simulation and visualization, Remote simulation and visualization means that both hybrid simulation and visualization. the simulation engine and any animation generation Local simulation and visualization (S&V) means, engine are located and execute remotely, on the that the simulation engine and visualization compo- server-side (Bencomo, 2004; Holzinger et al., 2008). nents are downloaded seamlessly by the client to the Access to these is through a browser on the client- user’s local computer, so that the graphical interface side. This approach can be considered a job request and the simulation engine coexist in the same envi- on a batch processing system. Parameters are submit- ronment (i.e., within the browser) shifting the re- ted to the simulation engine through the Web server, sponsibility for execution completely from the server and results are returned to the user once the simula- to the client, making the server a central distribution tion has finished running (Myers, 2004). Communi- point to the simulation but performing no real work cation between the graphical interface in the browser (Byrne et al., 2010; Bencomo, 2004). and the simulation engine is carried out using, for example, Common Gateway Interfaces (Morilla For the development of these simulations, Java is et al., 2001; V, 1996), sockets (Narayanan et al., currently the only real possibility for providing a 1999), Java remote method invocation (RMI), Ja- wholly independent hardware platform, although vaBeans, Common Object Request Broker Architec- there is some study on the viability of using multi- ture (CORBA), remote procedure call (RPC) or via media tools, such as Macromedia Flash, for the front-end applications for simulator software (Byrne simulation of real processes (Bencomo, 2004). et al., 2010; Bencomo, 2004). Web-Based Tools for System Dynamics Simulation 289 Figure 2. Basic configuration post initial loading phase (source: own elaboration based on Byrne et al., 2010) Fig. 3 shows the basic remote simulation and visual- of the hybrid simulation and visualization approach ization configuration, after the initial loading phase. is where the visualization/animation engine is used During this loading phase, the user opens a browser on the client-side to “build” the simulation model and navigates to a Web page and a basic interface through an animated interface, and display the re- is displayed in the browser. Both the simulation en- sults, without tying the animation to the simulation gine and any visualization/animation engine reside as the model is executing (Byrne et al., 2010). on the server-side, and are interfaced with through Table 1 summarizes the basic characteristics of pre- the browser. There may be a more advanced configu- sented categories of Web-based simulation with ration in which, for example, a database might be a special focus on their advantages and disad- present on the server-side (Byrne et al., 2010). vantages. By combining the approaches of remote simulation Finally, it is worth emphasizing that, apart from and local visualization, hybrid simulation and visual- the architecture of WBS applications, the Web-based ization, can be created that yields the benefits of both simulation is associated with such issues as (Byrne (Miller et al., 2000; Myer, 2004; Whitman et al., et al., 2010): 1998). In this approach, the simulation runs remotely on a simulation server, and when the user connects model repository – which concerns the applica- to the server through a WWW browser, a visualiza- tion of a server-based centralized repository that tion/animation engine is downloaded to the client- can be used to store simulation models. This al- side (Fig. 2) (Myers, 2004). A dedicated data con- lows for the ability to rapidly disseminate models, nection may be established back to the server, results and publications; in which the results of the simulation are transferred Web-based simulation documentation – which to the client-side allowing the visualization engine relates to the efforts to provide on-line documen- to display results to the user in a dynamic nature. tation to existing simulations including descrip- This data can change continuously, delayed only tion(s) of modelling components, results of out- by the executing simulation model and the latency put analysis for a set of inputs, and animations present on the network connection. This approach displaying simulation modelling results. Such is typically carried out by utilizing a Java server documentation can contain any or all the follow- and Java applets (Myers, 2004), but may be carried ing elements: text, images, audio and video out using other methods. Another implementation (Page, 1999). 290 Małgorzata Łatuszyńska Table 1. Comparison of WBS categories (source: own study based on Byrne et al., 2010; Bencomo, 2004) WBS Examples of Synonyms Advantages Disadvantages category applied technology Local Local simulation Java applets The network latency The power and flexibility of simula- and animation Macromedia Flash between the user and the tool are minimized, as it re- tion and Local simulation the simulator is redu- lies on the power of the client visualiza- visualization ced to nothing.