Landmark Paper Reprise – a Complete Interactive Simulation Environment Gpss/360–norden

Norden's expanded and interactive version of GPSS/360 has been extensively improved through new data entry and storage capabilities, a a new report generator, selective output display, and HELP blocks to enable model manipulation and to provide a a "window" to view the simulation during its progress. The data entry and manipulation system allows the user to input and display matrix savevalues through an IBM 2250 Display Unit. Titles may be placed on rows and columns to simplify the location of data items. A A less elaborate system was developed for remote terminal and batch mode data entry. The user can witness the progress of the simulation during the actual model execution• He then has the option to stop the simulation at any time, change parameters controlling operation of the model, and resume running of the model• This interactive feature opens vast new horizons for the world of simulation since with the appropriate equipment moving displays can be produced. BACKGROUND ON DEVELOPMENT AND REQUIREMENTS OF SIMULATION LANGUAGES Simulation is the newest and most conceptually sophisticated Operations Research technique• It must operate along two opposing major fronts. These are involvement in technique development as contrasted with application to specific problem areas. Unfortunately, the parallel technique development of simulation concepts and sufficiently powerful simulation languages has detracted from the building up of interfaces with those fields of potential applications. Furthermore, the resultant conflict of this duality has inhibited adequate recognition of simulation as evidenced by the lack of noticeable experimentation and application by industrial O.R. departments, university O.R. departments, computer mainframers, and management. Responsibility for the lack of acceptance thus caused lies largely within the field of simulation. Though long-term evolution has resulted in the existence of the necessary *Donald Ingerman, Currently with Bell Labs., New Brunswick, New Jersey **Kenneth Simon, Currently with IBM, White Plains, New York 260 techniques, the process has been too slow, and has left too many discouragements in its path. This is due to the fact that special interests internally have not devoted the time and resources necessary for systematic development. This evolution, resulting in simulation languages, has chronologically occurred as follows: . . special purpose languages written for unique applications, such as network and economic simulators. • • semi-general languages composed of simulation subroutines written in programming languages such as Fortran or Algol. • • truly general purpose user languages, such as GPSS, Simscript and Simula. creation of a a simulation environment exhibiting real world capabilities enabling a a system expert to create, modify and experiment dynamically with a a model of his system in a a manner consistent with the normal operation of the system. Orginally, the general purpose simulation languages were not very powerful due to lack of adaptability to problem areas and poor com-