Object_Oriented Modeling as an Instrument for analyzing a Film Processing Plant
From Proceeding of European Simulation Multiconference,ESS94, Barcelona, June 1_3 1994
P. Giribone

MODELING TOOL

In developing this model, it was always necessary to consider that it would probably be interfaced in the future with a scheduling system based on artificial intelligence techniques. Therefore, special attention was focused on the modular design and expandability of the model. This is why there was a tendency from the very beginning to develop a simulation based on an object_oriented approach.
The author is currently developing different scheduling applications using AI and operates in general with KBS. These systems normally refer to C++ as the interface tool.
The OS/2 release of MODSIM was selected as the modeling tool for the specific problem. Theoretically, this language offers special advantages for our specific case because it can be interfaced with subsequent scheduling modules and can produce file objects directly in C++.
Since the simulation product utilized is oriented towards industrial applications, the powerful graphic features offered by MODSIM can be used to streamline the data entry phase, to evaluate results and to screen dynamic processes; thus the simulator can be used easily and directly by plant personnel.
An alternative was also considered involving the direct use of C++ through libraries which had already been developed in the past by the author's work team for this type of problem. In fact, the author is part of a research group which normally uses general purpose languages (C++, C, Pascal) to model complex plants; this general line of action is possible and economically feasible thanks to the previous experience acquired from numerous concrete industrial applications.
Among other advantages, the use of general purpose languages offers improved running speed (and therefore reduced experimentation time), enhanced portability in different operating systems and greater useful service life of the modules developed for the specific applications. In fact, an analysis of the sector indicates that general purpose languages can maintain themselves on the market, guaranteeing complete compatibility with the previous releases for at least twice the time period relative to the languages developed for the simulation.
However, the desire to verify MODSIM capacities to interface with the C++ modules acquired from advanced applications (KBS or even Neural Networks) made it necessary to choose the latter. For the specific case, the delivery terms to develop the model, as established by the industrial representative, were not very demanding. The decision to use the OS/2 operating environment was dictated only by the contingent availability of the internal hardware resources. This meant that the most recent generation of personal computers, each with a 12 MB RAM, could be used to develop the work.
In fact, the potentials of the simulation tool used remain partially limited by the hardware equipment used, thus leading to increased running time; in spite of this, the fact that the code can be transferred into a UNIX environment means that a final release can be offered in a more interesting industrial environment.
From this point of view, the structure of the graphic module obtained is very important. In fact, this tool is used to condense the entire graphic part relative to drawings, windows, switches, etc., into an ASCII file; therefore, this system guarantees immediate portability from the OS/2 operating system to the UNIX environment.
Thus, the entire model could be developed within a specific low_cost environment. Furthermore, it was also possible to perform the experimental part within such an environment, while supplying an industrially powerful tool at the same time that can be immediately transported to workstations.
Obviously, the graphic potential offered by this tool can be implemented to perform a logical check on the first phase of the model; however, this must be followed by a statistical analysis of the data to validate the model. A comparison with other languages oriented towards simulations also provides interesting insight. Over the last few years, the author has developed simulation models using SLAM and SLAM II as well as Simscript (the Modsim predecessor).
In reality, the problem of languages oriented towards simulations may be expressed in terms of: model development speed, duration of the service life of the product and the capacity to go into detail during modeling.
While all the dedicated languages concentrate on simplifying and accelerating the modeling phase, unfortunately, it is often quite a complex task to adapt industrial situations to models built with these tools. The new generation of these languages operates within a slightly less modular framework compared to tools such as SLAM, Simfactory, etc.; however, it ends up reproducing the structure of existing multipurpose languages (Modula 2, C++, Pascal Object Oriented) in a very faithful way, usually adding a set of interesting graphic and statistical utilities which are certainly quite useful from a simulation point of view.
In fact, the author also agrees that it does not make much sense to talk about object_oriented languages, but rather a programming philosophy aimed at objects; while the OOD is undoubtedly the modeling technique for the future, because of its ability to produce highly flexible tools, it is very difficult to imagine that the many different tools currently being developed wil offer major improvements in creating simulators for industrial applications.
On the other hand, it can be said that the situation is totally different for graphic interfaces, which are evolving very rapidly in terms of interactions between users and model and also in terms of the possibility (though to a lesser degree up to now), of developing complex animation with relatively simple procedures. In this particular application the use of a pre_ determined language has certainly been very rewarding.
Another very important element to be considered when developing this type of application for industrial situations refers to products which are very compatible with company policies in terms of the type of language and the type of available hardware instruments. In fact, for companies which consider the simulation to be an important instrument, there is a tendency to standardize the model development tools to guarantee maintenance and updating. Over the years, this has led to the continued use of obsolete tools also in advanced applications where it would have been much more effective to use languages equipped with modern features.
External routines in C are linked to high_level programming languages (like G2: expert system), through the construction of data conversion procedures which guarantee an exchange of information. In this type of application, we limited ourselves to checking the possibility of transferring the information in the simulator to the main system, since the transposition of knowledge is still in the initial phase.

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