paper. 1 INTRODUCTION. Currently, the development of the information and. communication technology is dominated by the Internet. Web-based or distributed ...
CONCEPT AND COMPONENTS FOR A WEB-BASED SIMULATION ENVIRONMENT (WBSE) Frank Seibt, Marco Schumann, Jürgen Beikirch Department of Simulation and Graphics (ISG), Computer Science Department Otto-von-Guericke-University Magdeburg Universitaetsplatz 2 D-39106 Magdeburg email: {seibt | maschuma | beikirch}@sunpool.cs.uni-magdeburg.de
KEYWORDS Simulation Environment, WWW, CGI-Technique, Java, Presentation
http: //www.cs.uni-magdeburg.de/~seibt/labor/labor.html the Canal-and-Lock System (Lorenz, Schriber, and Seibt 1997) can be found as an example of a complete Webbased simulation and animation study.
ABSTRACT The growing global use of the World Wide Web (WWW) and the rising acceptance of Intranet-based systems have a strong influence on simulation, animation, and visualization applications. They can be used globally or within defined domains of the network. But currently existing simulation and animation systems are typically platform-dependent and are not designed to work in the Internet or an Intranet. In this paper, a concept and some components for a Web-based simulation environment (WBSE) will be presented. With this simulation environment, an easier and faster integration of simulation, animation, and visualization techniques and tools into the Internet will be supported. The possibilities and problems of the used techniques will be shown in this paper.
1 INTRODUCTION Currently, the development of the information and communication technology is dominated by the Internet. Web-based or distributed solutions and systems become more and more attractive. The major aspects of the influence of the Internet are platform independence, maintenance minimization, reusability, and interoperability. At the University of Magdeburg, Web-based simulation and animation is the subject of several projects. For example, a Web support for a simulation and animation course can be found at http://isgnw.cs.unimagdeburg.de/~pelo/sim1d/sim1.htm. The results of another project which enables the user to run own GPSS/H models on a remote server can be tested at http: //simsrv.cs.uni-magdeburg.de/cgi-bin/simwww.rungpss (Dorwarth, Graeßner, and Lorenz 1996). Furthermore, at
Figure 1: A schematic representation of the Canaland-Lock System In these projects, specific Web support and presentation of simulation and animation have been implemented. In this paper a further logical step will be presented: the concept and the components of a Webbased Simulation Environment (WBSE). For some of the components, prototypes have been implemented to recognize and demonstrate the advantages and problems of such an environment based on currently available Web techniques. In section 2, typical steps of a simulation study will be presented. Section 3 presents the developed concept for a simulation environment in the WWW. In section 4 the design of some necessary components for this environment and some prototypes will be presented. In section 5, remaining problems of the developed concept, components, and the used techniques will be discussed.
2 SUPPORTED STEPS AND FUNCTIONS IN A WBSE A WBSE has to support two different types of simulation applications: •
The classical steps of a simulation study, and
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New approaches to Modeling and Simulation (M&S) based on cooperative work of distributed
Web clients and users, for the "Collaborative M&S". (Zeigler, Sarjoughian, and Vahie 1997) The following typical steps in a simulation study (Law and Kelton 1991; Banks, Carson, and Nelson 1996) can be distinguished and supported by the Web in the following ways: 1. Description of the real system which is going to be modeled, simulated, or optimized and definition of the project goals. This can be supported by the Web in a classical way, by presentations of the real objects, processes, or services in static WWW pages. 2. Acquisition of input data by measurement, estimation, and calculation of values of the real system, and determination of the appropriate distribution functions and their proper parameters. The transfer of files with input data can be done easily by the Internet. The use of new and already existing Java-based statistical tools in the Web-based simulation environment is planned. 3. Creation of a logical or artificial model of the real system and implementation into a simulation system in order to create the simulation model. The creation of such a model is problemdependent. It can be supported by presenting all relevant information in a HTML-page, and by allowing the creation of the model to occur on the same page. 4. Verification and validation of the simulation model. This step can also be supported by collecting data of the project and presenting it in an overview style page. In addition to this, simulations with deterministic data sets can be executed by the CGI-script technique (Dorwarth, Graeßner, and Lorenz 1996). 5. Planning and running of the simulation experiments with the model. This can be done completely by the CGI-technique. 6. Processing, compression, interpretation, presentation, recording, and comparison of the generated results of the model and, if possible, creation of meta models. As in (Lorenz, Schriber, and Seibt 1997), the presentation and animation of simulation results in the Web can be implemented again by using the CGI-technique. 7. Comparison of the simulation results with the real system and suggestions for changes in the real system, based on the simulation results. The presentation of the results and reports can be done in the Web, or the data can be transmitted easily by the Internet. For example, in the simulation environment TESSTM (The Extended Simulation Support System) (Standridge,
Pritsker, and Stein 1987) the steps model input, execution of the simulation, statistical analysis, presentation of results, and animation are supported. An automatic recording of simulation results is guaranteed by the system. For developing a simulation study, a fixed set of prescribed platform-dependent software tools have to be used. Helpful is the usage of platform-independent software tools to support simulation and animation in the Internet by a WBSE. In comparison to currently existing environments, the structure of a WBSE must be modular. "Commercial available simulation tools and methodologies are primarily single user tools that provide inadequate support for collaborative team-based environments." (Zeigler, Sarjoughian, and Vahie 1997) The WBSE will be open for concurrent engineering and will at least include prototypes for collaborative use of simulation models. By the special possibilities of the Web, the collaborative work can supported by a WBSE.
3 CONCEPT OF A WBSE On the basis of the results described in (Lorenz, Schriber, and Seibt 1997), a concept of a WBSE has been developed. The simulation environment presented in this document will support the steps 3, 5 and 6 of a classical simulation study. For the concept of the WBSE, it is first necessary to classify different developer and user groups into: •
WBSE system designers,
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WBSE component constructors,
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model designers, and
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model users.
A similar classification of developers and users of modular simulation environments can be found in (Standridge et al. 1996). The architecture of the planned WBSE is generally a client server structure. The entire WBSE, with its different components, will reside on the server side. The planned WBSE is an open system with three options of installation: •
a globally installed WBSE available for all Web users,
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WBSE’s installed in corporated intranets, and
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components installed on local machines.
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components for analyzing input and output data, e. g. statistic programs,
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components for supporting a simulation expert, and
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components for collaborative M&S.
Another classification of components by software engineering aspects can be:
Figure 2: Creation of a Simulation Study with the WBSE The components of the WBSE can be allocated to the same or to different servers. Web clients have access to the components by using Web browsers. The WBSE will especially support model designers. If model designers want to implement new presentations in the Web, they can access to appropriate components of the WBSE. They call up HTML pages with different content and functionality: •
General information,
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Model construction forms for text-based simulation and graphical model construction tools,
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Creation of parameter input forms for prepared models, started by CGI-scripts on the simulation server,
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Calling up applets for simulation, animation, and visualization, executable on the client’s computer,
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Recording of simulation results by a database.
With these components the user performs new presentations. After the installation of the prepared presentations on a simulation server, the model users can access the newly developed presentation by only using a Web browser. The architecture of such created presentations is comparable to that in (Lorenz, Schriber, and Seibt 1997). The components of the WBSE can be classified by user aspects in: •
components to support modeling activities, such as model development, model input, and selection and usage of simulation systems,
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components for developing model-user interfaces, such as input forms and output records,
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components for presentations, such as visualization of simulation results, and animation,
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components for database access, such as the recording and comparing of input and result data sets,
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HTML-pages with input forms and CGI-scripts,
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Java-applets,
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Java-programs, and
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special designed platform dependent tools.
One essential property of the WBSE is the execution of simulation runs on a remote simulation server. In the prototype for the WBSE, this is implemented by a CGIscript which starts a simulation system by a command line. The WBSE have some benefits in comparison to classical systems. For example, the modular structure of the environment allows an exchange of used software tools. New components can be added to, or obsolete components can be removed from, the system. Additionally, parts of the WBSE can be located on different servers, and presentations, made with the WBSE, can be installed into the Web. Platform-independence is one major benefit of the WBSE. The concept of the new WBSE supports the collaborative work of a model designer team, by allowing each team member to access the components and data as a client.
4 COMPONENTS OF A WBSE To implement the concept of the WBSE, different components, such as the creation of input forms, the generation of CGI-scripts, the presentation of simulation results, the creation and inclusion of animations, the recording and comparison of simulation results by using databases, the support of simulation experts, and the implementation of the communication between these components, are needed. The design and some prototypes of these components will be presented in this section of the paper.
Figure 3: Planned components of the WBSE
4.1 Model development In the component for the model development (MDC), the model developer can create new models or select an existing simulation model. In this component the developer has to define the input and output interfaces of the model. This is to specify the structure of •
the input parameters or data,
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the input files,
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the output files, and
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the animation trace files.
After the model is defined, the model developer has to specify the simulation system which will be used in the simulation study. The MDC will offer a selection between adequate commercial simulation systems. Along with these systems, a new Java-based GPSS system, javaGPSS, developed at University of Magdeburg (J. Beikirch), can be used. This system generates a Java program from the GPSS model. The program has to be compiled and then executed to run the simulation. Results of such a simulation will be transferred (e. g. to the 2D Animator Skopeo) by pipes. The different simulation scenarios and the executing server have to also be defined in the MDC. The execution of the simulation will be controlled by a central CGIscript (CGIS). The appropriate code in the CGIS for the part of the new Web-based presentation defined by this component will be generated automatically by the MDC.
Figure 4: Screen shot of the input forms creation component
4.3 Presentation of results Once the simulation is done, the results have to be graphed. The component presentation of results (PRC) available in a first version allows the representation of results as a business graphic. The approach uses the LightLib library for Borland Delphi developed by the DFL Software Inc. A small program (GraphIt!), created by M. Schumann at the University of Magdeburg, translates an ASCII input file generated by a simulation model into function calls of the LightLib library. The program is implemented in Delphi and installed on a web server. It can be activated by using CGI technique. The executed CGI script sends back an HTML page including the generated picture.
4.2 Data collection In the component data collection (DCC) of the environment, the model developer can easily create input forms of new presentations by simple drag and drop actions. The DDC is implemented in Java and can be used in any Java-enabled Web-Browser on any platform. The communication between the input form and the simulation model will be done by a file, which has to be defined by the model developer. The code in the CGIS will be generated automatically by the DCC, based on the specifications made by the model developer.
Figure 5: Process of generating pictures
4.5 Recording of results In this component, the recording of simulation results (RRC) in a database will be organized. The access to the database will be implemented by the controlling CGIS. Therefore, it is necessary to define an additional interface with a simulation model. The goal of such a recording is to accelerate a new presentation of older simulation results, and to allow comparisons between results of different simulation runs of the same model. The appropriate code in the CGIS will be generated by the RRC, such as in the other components. Figure 6: Example of a generated picture Text-based results of the simulation model will be included in the resulting HTML page by also using the CGI-technique. The inclusion of the code for presentation of results in the CGIS will be done automatically by the PRC.
4.4 Animation In one component of the WBSE the animation (ANC) of simulation problems will be enabled. This will be done by the 2D Java-based animation system Skopeo (Lorenz and Ritter 1997). This animation system is trace-driven and needs a layout and trace file for an animation. The simulation developer must ensure that these files are generated by the model or created manual, for example with a layout editor. Some examples of animation by this system are available at http://simos2.cs.uni-magdeburg. de/Skopeo/Ani.html.
4.6 Simulation expert support In the WBSE an additional component to support a distant simulation expert (SEC) will be implemented. The SEC will enable the access to models and generated trace data. The simulation expert will get an index of existing files, and he or she can select the one he or she wants to analyze. In the next step he/she can modify the trace data local by own programs to investigate special properties of the data. Another step is the modification of simulation models and the remote execution of these models to get additional trace data. Like in all other components, the code for the CGIS will be generated by the SEC.
5 OPEN PROBLEMS IN DEVELOPED CONCEPT COMPONENTS
THE AND
During the design and implementation of the concept and components of the WBSE, following limitations and problems appeared: •
Java-based applications run slower in comparison to platform-dependent programs. Especially when an animation is running, or a simulation based on javaGPSS is executed, the slower running can be observed.
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A general limitation for the use of simulation systems in the WBSE is: a simulation run must be operable by a command line.
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The forms of interactions of a created Web-based presentation with the WBSE are limited in the usage of the CGI-technique in running the simulation model on a remote server.
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The usage and acceptance of the presented system for commercial use is uncertain. For this application of the WBSE, questions about security and copyrights are especially important.
Figure 7: Screenshot of a Skopeo animation Additionally, the use of a new 3D VRML-based animation system is planned. A prototype of this 3D system is under construction. The code for including an animation in a simulation study for the CGIS will be generated automatically by the ANC.
6 CONCLUSIONS AND OUTLOOK
Support System. In Proceedings of the 1987 Winter Simulation Conference. 238 - 246.
In this paper a concept for a Web-based simulation environment has been presented. For this concept some prototypes of components have been implemented. With this simulation environment an easier and faster implementation of simulation, animation, and visualization into the Internet or an intranet is supported. A model developer can create Web-based simulation studies and appropriate presentations in an easy way. A central CGIscript, which controls the simulation study including a presentation, will be generated by the components of the WBSE based on the specifications made by the model developer. In this way simulation models, animations, and complete presentations can be presented platformindependent, inner-corporate, or world-wide.
Standridge, C. R.; J. F. Kelly; T. Kelly; and J. Walther. 1996. Progress in Modular Simulation Environments. In Proceedings of the 1996 Winter Simulation Conference. 714 - 720.
Future projects in the domain of Web-based simulation environments have to solve the open problems along with the search, designing, and implementing additionally required components of such an environment. It is also necessary to include other simulation systems like SLX, Siman, and ModSim, along with GPSS/H and javaGPSS in the WBSE. Generally there is the question for the commercial application of the presented techniques. How much work and what costs are needed for a commercial simulation service in the Web, based on a WBSE? Additionally the acceptance of such a service for a client must be established.
REFERENCES Banks, J.; J. S.Carson; and B. L. Nelson. 1996. Discrete Event System Simulation. Second Edition. Prentice-Hall, Englewood Cliffs, N.J. Dorwarth, H; H. Graeßner; and P. Lorenz. 1996. Simulation und Animation im World Wide Web. In Proceedings of the Simulation und Animation für Planung, Bildung und Präsentation '96 (ASIM). 173 - 184. Law, A.M. and D.W. Kelton. 1982, 1991. Simulation Modeling and Analysis. McGraw-Hill, New York. Lorenz, P. and K.-C. Ritter. 1997. Skopeo - A Platform-Independent System Animation for the W3. In Proceedings of the Simulation and Animation '97 (Magdeburg). 12-23. Lorenz, P.; T. J. Schriber; and F. Seibt. 1997. WWWBased Simulation Experiments and Presentations of the Canal-and-Lock System. In Managing and Controlling Growing Harbour Terminals, E. Blümel et. al. SCS Publishing House San Diego, Erlangen, Ghent, Budapest. 148-161. Standridge, C. R.; A. A. B. Pritsker; and C. W. Stein. 1987. A Tutorial on Tess: The Extended Simulation
Zeigler, B. P.; H. Sarjoughian; and S. Vahie. 1997. An Architecture for Collaborative Modeling and Simulation. In European Simulation Multiconference June 1-4 Istanbul, A. Kaylan and A. Lehmann [Eds.]. SCS International. K-3 - K-16.
AUTHOR BIOGRAPHIES FRANK SEIBT is a Masters student in the Department of Simulation and Graphics in the Computer Science Department at the Otto-von-Guericke University. His main research interest are in the designing and implementation of Web-based simulation tools and applications.
MARCO SCHUMANN is a Masters student in the Department of Simulation and Graphics in the Computer Science Department at the Otto-von-Guericke University. His experience in developing applications for the Internet includes a one-year-stay at the University of Wisconsin, Stevens Point. His main research interest lies in application of simulation methods in the field of factory planning, and optimization.
JÜRGEN BEIKIRCH is a Masters student in the Department of Simulation and Graphics in the Computer Science Department at the Otto-von-Guericke University. His main research interest lies in designing and implementing simulation systems.
