Web-Based Tools for System Dynamics Simulation

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 behavior of a system on a computer over extended periods of time. One of the computer simulation methods 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.

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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 example, 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).

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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 visualization 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).

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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. to execute the simulations effi- tion ciently, and some users may Local simulation lack the hardware needed for Client-executed this. simulation Remote Remote simulation Common Gateway Larger simulations Not good for observing dynam- simula- and animation Interfaces, can run on powerful, ic processes at work. tion and based on loading Java remote high-end computers It does not allow the user to visualiza- applets method invocation and the analysts can interrupt a running simulation. tion Server-side-based (RMI), get access to the results from any low- The client can only view pre- Web simulation JavaBeans, specified outputs at a specified solution end computer with Common Object a browser. time. Remote simulation Request Broker The developer requires a kno- visualization In addition to provid- Architecture ing a familiar inter- wledge of middleware technol- Remote simulation (CORBA), face, it works well ogies. Server- hosted Remote Procedure for adapting existing Long running simulations may simulation Call (RPC) sim-ulation products take an extended time to gener- Front-end applica- to a Web-based envi- ate output, especially under tions for simula- ronment. heavy load, resulting in the tion software Easier maintenance user having to wait long peri- for developers. ods of time or having the client timeout by waiting too long for a server response. The server can easily be over- loaded if all the responsibilities for simulation are placed on the server for several concurrent user simulations, or if there is a heavy need for, for example, interactivity, visualization data or numerical solvers. Hybrid Animation and Java server pages More powerful hard- The communication between simula- manipulation using (JSP) ware. the client and server is delayed tion and a Java data server Java applets Maintenance is eased by network latency, which visualiza- might be several seconds on Remote simula- ASP.NET with a centralized ap- tion tion/local visuali- plication. a wide area network. zation The workload on the Hybrid cli- server is reduced. ent/server simula- More user interaction tion by sending the animation/visualization por- tion to the client-side.

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The issues discussed in this section are common  experimenting on the model can facilitate under- for all simulation techniques. The differences in the standing of anti-intuitive behavior of complex processes of modelling and simulation conducted systems, by means of varying simulation techniques are first  cost of collection of data to carry out experiments of all a consequence of the very nature and the pur- on the model is relatively low, pose of these techniques (Behdani, 2012; Borshchev,  decision processes mapped by the model are close 2013). The sections below will present the substance to real ones to such an extent that they allow of the System Dynamics simulation modelling for forming an appropriate policy, and discuss the System Dynamics Web-based tools.  industrial system behavior is determined by its internal structure; therefore, most problems are 3 System Dynamics modelling and simulation internally generated,  real system behavior is so detached from the ideal System Dynamics is the simulation modelling tech- one, that each effort of improving the system be- nique used mainly for the analysis of poorly struc- havior, is justified. tured problems, with numerous interrelations among On the basis of the premises mentioned above, J.W. elements. It originates from cybernetic approach Forrester took a peculiar approach to modelling to system analysis and allows for describing espe- and analysis of system behavior, which is based cially complex systems in the form of interactive and on the system concept in the way that it is more combinatory relations. Its theoretical foundations closely related to practice than theory. J.W. Forrester were created by Forrester and his colleagues from the considered System Dynamics as a facilitating tool Massachusetts Institute of Technology (Cambridge, for management of the highest level, in strategic MA, USA) in the '50's of the 20th century. Forrest- planning, where traditional management theory er's approach to industrial system modelling, the first is of limited effectiveness. application area for this method, is described in one of the earlier papers, entitled Industrial Dynamics During above 60 years, the interpretation of System (Forrester, 1971). Seven premises of the System Dynamics underwent certain modifications, but it Dynamics application are presented there: managed to preserve its theoretical assumptions,  decision making process belongs to the class based on three scientific disciplines, that is, tradi- of control problems with information feedback, tional management theory, cybernetics and computer simulation (Fig. 3).  intuitive judgement of behavior of industrial systems is unreliable due to their complexity,

Traditional Theory Cybernetics Computer of Management Simulation creation creation selection intellect intellect the rules structure of

quick calculations dynamic behavior the rules of information information of rules the informtion, experience, experience, informtion, and strategy MODEL improvement

Figure 3. Methodological background of System Dynamics (source: Łatuszyńska, 2005, p.32)

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Traditional management is a process which consists entire system and to help to use this technique with- of continuous decision-making. In a highly simpli- out necessary knowledge of mathematical back- fied perspective, this process begins from the obser- ground. The first tool was a special programming vation of external world, identification of purposes, language called DYNAMO created in the 1960s. connections and information streams. As a result, DYNAMO was a typical high-level language that imagined models are created, and the future behavior was not quite friendly for users of low IT sophistica- of systems in various conditions is predicted based tion. Later, many other tools appeared on the market on these models. that now support the creation of System Dynamics models. The most difficult part of this process is the selection of information and then finding the right course There is a constantly updated list of available tools of action which should ensure that defined goals on the System Dynamics Society web page (SDS, are met. Surprisingly, quite often, mistakes in man- 2017). The list also contains tools that enable, to a agement stem not so much from incorrect view greater or lesser degree, the creation and/or execu- of particular cause-and-effect chains, but from wrong tion of System Dynamics models on the Web: understanding of system dynamics as a whole.  AnyLogic by The AnyLogic Company Cybernetics, which bases on feedback theory, puts (anylogic.com), a strong emphasis on dynamic interactions between  Consideo iMODELER by Consideo GMBH system elements and provides tools allowing for (www.consideo-modeler.de), better understanding of system behavior. It gives  Forio Simulations by Forio Corporation guidelines for distinguishing between important and (www.forio.com), unimportant information in a given context, and then  Insight Maker, created by S. Fortmann-Roe and for structuring and formalizing it in a mathematical G. Bellinger, hosted by Give Team model. (www.insightmaker.com), Finding solutions for such models with non-linear  SimiLive – service for Simile simulation software relationships (often made of numerous equations) by Simulistics Ltd and predicting the results of analyzed decisions (similive.simulistics.com), by means of such models are generally only possible through use of appropriate numerical methods.  Simupedia Studio - plugin for Simantics System In case of System Dynamics, the method of choice is Dynamics by VTT Technical Research Centre computer simulation based on constant step method. of Finland and Semantum Oy (sysdyn.simantics.org/; www.simupedia.com), As a result, System Dynamics provides a rationally founded tool base for the construction of models,  Sysdea of Strategy Dynamics Ltd, which should produce information about behavior (sysdea.com). of systems as a whole. Theoretical assumptions AnyLogic simulation software supports system dy- and detailed rules of System Dynamics modelling namics, agent based and discrete event modeling. and simulation have been defined in multiple publi- It allows making hybrid models. Since AnyLogic cations, including (Krupa, 2008; Meadows and models are 100% Java applications, they can readily Wright, 2008; Łatuszyńska, 2008). be published as web applets. With AnyLogic, the whole model will automatically run on the client

machine within the applet. It is enough to send 4 Web-based tools for System Dynamics a ready-to-run simulation with GUI and experimen- simulation tation capability to anyone with a browser. Many SD

applets generated by AnyLogic are published From the beginning of System Dynamics, many on website www.runthemodel.com. tools have been developed to support specific for this technique modelling of feedback loops, nonlinearity, and time delays that influence the behavior of the

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Table. 2 System Dynamics Web-based tools (source: own study)

On-line Case courses WBS Technology/ Tool name Logo Licensing Main features studies or docu- category Language available menta- tion Proprietary, commercial, S&V of existing free Personal Java web models with an op- AnyLogic Local yes yes Learning applets tion to enter input Edition for data education Building, S&V of new models. S&V of existing Consideo Proprietary, JavaScript models with an op- iMODEL- Local yes yes commercial Adobe Flash tion to enter input ER data and make structural changes to the model JavaScript, REST-based S&V of existing Forio APIs Proprietary, models with an Simula- Hybrid Forio Sim- yes yes commercial option to enter tions Lang, Python, input data Julia, R, Ven- sim Building, S&V of new models. Free, Insight Insight S&V of existing Maker Public Local JavaScript yes yes Maker models with a lim- LicenseL ited option to enter input data Proprietary, commercial, S&V of existing Free evalua- JavaScript models with SimiLive tion license Hybrid C++, Prolog, yes no an option to enter limited to 25 Tcl input data model elements S&V of existing Simupedia Eclipse Public JavaScript models Hybrid yes yes Studio license (EPL) Modelica with an option to enter input data Building, S&V of new models. Proprietary, S&V of existing commercial, models with an op- Sysdea Local JavaScript yes yes a 30-day free tion to enter input trial data and make structural changes to the model

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Consideo iMODELER offers quantitative and quali- Sysdea is an on-line, browser based, system dynam- tative modeling. This tool allows to build web-based ics tool. It is easy to use, has extensive documenta- models and is free for educational purposes. It runs tion and easy model sharing options. Sample models on any modern PC, Mac, Smartphone or Tablet- are available on the website: strategydynam- Computer as a web-based application (iMODELER- ics.com/info/system-dynamics.aspx. Service) or alternatively as an installed App Launch- Table 2 includes additional information associated er for Win, Mac or Linux. Sample models are with the above-mentioned Web-based tools for Sys- available on the website: www.know-why.net. tem Dynamics modelling and simulation, specifying Forio Simulations allows building web-based inter- the used technology, the WBS form and the main faces to already developed models, and provides features. a library of interactive environments for users. Only Consideo iMODELER, Insight Maker and The software is web hosted, with a commercial use Sysdea provide an opportunity to create both simula- license, but provides a number of options for low tion models and their simulation and visualization cost and no cost publication and proliferation via a browser. The remaining tools are first of all of models and model results. Sample models are used for publishing in the Internet the models created available on the website: forio.com/simulate. by means of some simulation software. All of them Insight Maker is a multi-method simulation and allow changes in the model input data prior to the modeling platform that runs completely in a web simulation. Additionally, some of the tools permit browser. It supports causal loop diagrams, rich pic- changes to the structure of the completed models tures, dialogue mapping, mind mapping, stock & (iMODELER, Sysdea). flow simulation models. It enables to build, run and Undoubtedly, the combination of System Dynamics share System Dynamics models without download- simulation with WWW will help avoid many limita- ing or installing a single program. Sample models tions typical of a traditional simulation constructed are available on the website: insightmak- by means of a dedicated simulation software, espe- er.com/tag/Sample-Model. cially when applied for educational purposes. SimiLive is a web-based model execution service The limitations mainly refer to: high outlays and for Simile System dynamics software. It allows considerable cost of simulation modelling tools models built in the Simile modelling environment (prices of core System Dynamics software, like to be executed on a web browser. It provides a sim- iThink/Stella, Powersim Studio or Vensim range ple way to publish any model, including parameter between 1 000 to over 7 000 euro, depending on the data and visualization tool setup. The model diagram version), as well as the hermetic nature of the simu- and visualization tools have been customized to drag lation expertise (which seems to be available only and zoom via a touch screen interface, so the service to experts and experienced users of simulation mod- is ideal for showing and executing models on mobile els (Maciąg et al., 2013, p.314). On the other hand, devices. Sample models are available on the website: WBS has its weaknesses – these are discussed in the similive.simulistics.com/demos. next section of this paper. Simupedia Studio is a plugin, which enables the generation of interactive Simupedia web pages. 5 Advantages and disadvantages of WBS The power of Simupedia derives from the open source modelling and simulation platform called Web-based simulation has many benefits in compari- Simantics. The system has client-server architecture son to the classical simulation systems, and many with a semantic ontology-based modelling database authors attempt to identify these, see (Miller et al., and Eclipse framework-based client software with 2001; Bencomo, 2004; Kuljis and Paul, 2001; Mac- plug-in interface. Sample models are available on the iąg et al., 2013; Pidd and Carvalho, 2006; Whitman website: www.simupedia.com/Demo/#WorkRoom/ et al., 1998). Management.

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Byrne et al. (2010) lists for instance the following:  Wide availability - WBS application can be used  Ease of use – the process of simulation model from anywhere in the world with an Internet con- building is accepted in the simulation community nection and outside of normal business hours to be a fundamentally difficult, time-consuming without having to transport hardware or software. and error-prone one. Commonly known charac-  Versioning, customization and maintenance − in teristics of the Web is its ease of navigation and using a Web-based system, maintenance is mini- use. The Internet provides a familiar interface for mized. All modifications can be made through the both interacting with and controlling a simulation. server, enabling frequent modifications, customi- However, it seems to be very dangerous to make zations and updates to be made and instantly dis- an extrapolation from the ease of use of common tributed to the application, reducing error Web-based systems to WBS systems, as the typi- potential and eliminating virtually all on-site cal work and necessary features are different. maintenance.  Collaboration – WBS environments can support  Integration and interoperability  a Web-based collaborative model development, where people tool can integrate and interoperate with both ex- can communicate with each other from different isting and future Web-based applications, as well places to build the same simulation model over as Web-enabled desktop applications. the Web. Such collaboration can include monitor- Several disadvantages of WBS over classical simula- ing and debugging with the help from experts. tion systems have also been identified. Byrne et al. This approach may result in a reduction in simu- (2010) lists, for instance, the following: lation model development cost and time, over the  loss in speed − the user can experience loss use of System Dynamics simulation modelling in speed when interacting with the tool due packages such as Powersim, Stella/iThink to downloading time and network traffic (Suh, or Vensim, which are only used at a local ma- 2005); chine.  graphical user interface limitation − the interface  Model reuse - modelers suggest that model reuse provided by the Web as opposed to desktop simu- may in fact cost more than developing new mod- lation tools is limited, although this is starting els, as trust must be established through testing. to change with the evolution of multimedia au- The Web can support the reuse of existing simu- thoring tools for the Web, lation models very well by its distributed nature  security vulnerability − Web-based applications and the content management function like search are more vulnerable to malicious attacks than cli- machines and common data access protocols. ent-based applications,  Cross-platform capability - the Web allows to run  Web-based simulation application stability – an application on any Web browser on any oper- the stability of a WBS application can be affected ating system without compiling. This capability or disabled by, for example, the disappearance relieves the application developer from having of any site that hosts parts of the modelling envi- to worry about a client’s configuration. ronment (Kuljis and Paul, 2001),  Controlled access - access can be controlled to  licensing restrictions - if the simulation engine a Web-based simulation application through is developed using traditional proprietary simula- the use of passwords, and limited time-span action software, there may be license restriction is- cess can be allocated. Users who need access sues, as traditional software licenses of simu- to specific or limited areas of an application can lation packages only allow a single place usage be given access merely by being added to whereas a Web-based system must have the same a password list, instead of having their client ma- license model as a network license; this can be chines updated. overcome through the use of open source simulation software for the simulation engine.

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The shortcomings listed above as well as the specific proach taken by Web-based simulation so far, which nature of computer simulation as a research method has not changed from the classical approach to take can constitute a barrier for further development advantages of the new media. This mismatch is illus- of WBS. trated well in the Table 3. As Kuljis and Paul (2001) state. it is the mismatch between the Web main characteristics and the ap-

Table 3. Comparison between Web Features and Simulation (source: Kuljis and Paul, 2001, p.47)

Web Web - Based Classical Features Simulation Simulation

Common Standards Yes No Platform independence Yes No Interoperability Generally not supported Not supported Ease of navigation Varies Varies Ease of use Difficult to use Difficult to use No specialist knowledge required Specialist knowledge required Specialist knowledge required Not affected by change Affected by change Affected by change Unstructured Structured Structured

The Web is a truly democratic and non-exclusive of the format it is in (text, pictures and hypermedia). medium as is evident by the exponential growth Simulation uses data that is not generally accepted of Internet subscribers. The main reasons for this in a standard format and usually has to be provided are that the Web is easy to use and to navigate in a specific format (Kuljis, 1996). Modelling com- through, is forgiving (one cannot make unrecovera- ponents and rules of assembling these components ble errors), and is easy to publish on. The access also have to follow standards specific for simulation to the Web is widely available, does not depend software. Outputs from the simulation again follow on proprietary software, and so on. Simulation is different rules and vary in: what is reported, how it and always was a highly specialist application area is reported, at which stage of the simulation run (Web-based or not) − not easy to use. Some simula- it is reported, formats of output files, and so on. tion software does not have an obvious or consistent (Kuljis and Paul, 2001). navigational strategy (Kuljis and Paul, 2001).

The stability of the Web is not affected by the addi- 6 Conclusion tion of new sites, removal of existing sites, or any changes to sites. The stability of WBS, as it was The World-Wide-Web enables a distributed envi- mention before, can be easily affected or even disa- ronment for utilizing simulation tools. By using bled, for example, the disappearance of any site modern Web technologies, the transition to Web- that hosts parts of modelling environments (Kuljis based simulation is simplified. As the above short and Paul, 2001). review has shown, much has been done in the area The Web is a vast collection of often unstructured of WBS  also in the context of System Dynamics information that is always available and accessible simulation technique. (as long as the server holding it is ‘alive’), regardless

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