DEOS: a new object-oriented simulation environment. A validation study. A. Anglani, P. Caricato, A. Grieco, F. Nucci, M. Pacella Dipartimento di Ingegneria dell’Innovazione - Università degli Studi di Lecce Via per Arnesano, Lecce, 73100 Italy, e-mail: antonio.grieco@unile.it Abstract Simulation is a widely used technique for modelling manufacturing and other types of complex systems. Software packages, including both general-purpose and specialised environments designed to simulate manufacturing systems, have increased the popularity of simulation. Object- Oriented approach offers significant potential over existing common process-oriented simulation software. In this paper, a new object-oriented discrete event simulation environment, DEOS, is presented and examined. The paper proves the reliability and credibility of the software tool by means of a comparison to a diffused and accredited simulation package such as ARENA. A simple job shop system has been adopted as test case, and both DEOS and ARENA models have been realised. A statistical validation method based on seven performance measures compared using the analysis of variance ANOVA has been adopted. 1. Introduction Due to the rapid advance in computer technology, simulation has emerged as a significant tool for modelling manufacturing and other types of systems in modern industries. Various software packages, including both general-purpose simulation and specialised packages designed to simulate manufacturing systems, have been developed. Essentially, they consist of a collection of functions and procedures accessed trough high- level constructs. The use of high-level constructs allows a more natural modelling phase of a system than the one obtained with traditional general- purpose programming languages. The validity of these languages is proved by various applications available in literature [1,2]. Nevertheless, these packages commonly referred as process-oriented, have their drawbacks. Since their abstractions are suitable to represent only independent entity flows among processes, they lack flexibility and are inadequate to model a co-ordinated behaviour among different components. In general, it is broadly established that traditional process-oriented programming methodologies are not convenient to cope with flexible, maintainable and complex software. Object Oriented (O-O) programming has proved to be a powerful technique with respect to modelling and design of complex systems and it offers significant potentials over other popular simulation language in several respects [3]. The O-O approach has advantages connected with handling complexity, reusability, extendibility, modularity, and data abstraction, which enables it to manage software requirements more effectively than traditional programming approaches. Promoting reuse of software blocks and shortening the software development time-cycle are particularly significant features of the O-O technique. An object-oriented approach is particularly promising for the development of simulation software. Although commercial and academic O-O simulation systems have recently emerged, such as SIMPLE++ (by AESOP [4]) and MODSIM (by CACI [5]), a new environment named DEOS (Discrete Event Object Simulator) is proposed in this work. The aim of the presented environment is to provide a research environment for O-O design, analysis, and management of complex systems. The features of the proposed environment are basically different from the mentioned commercial tools. Since DEOS consists in a pure message-passing environment it allows an easy modelling of the co- ordinated behaviour among different components. Moreover, DEOS combines interactive simulation model design, object manipulation, simulation and output analysis to provide an intuitive modelling capability. The aim of the new environment is to allow the user to easily design simulation model by means of two main features. • The first concerns software maintenance: visual code is simpler and easier to interpret. • The second is relative to software modifications: a new layout simulation requires only inserting additional objects into the system and specifying the new relationships among them. Simulators on the market do not support a simple and direct message passing modelling. For example in SIMAN [6], a SCAN block, that checks conditions, and a SIGNAL block, that can activate the WAIT block are provided. This simulator, however, does not use any message passing among objects but global variables that can be directly accessed in any simulation flow. In this paradigm, models (i.e. sequence of SIMAN blocks) can become so interdependent that a small change has a massive ripple effect. Moreover, MODSIM, one of