Ören – SCS M&S Magazine – 2011 / 2 (April) 82 The Many Facets of Simulation through a Collection of about 100 Definitions Tuncer Ören Ph.D., Emeritus Professor School of Information Technology and Engineering (SITE) University of Ottawa, Ottawa, Ontario, Canada oren@site.uottawa.ca ABSTRACT About 100 definitions of simulation are collected and classified in nine types as a basis for a forthcoming critical review of definitions of simulation. BACKGROUND Due to the advent of the modeling and simulation (M&S) discipline in almost all branches of knowledge (Ören, 2009a), the development of its body of knowledge becomes of paramount importance and urgency. In the October 2010 issue of the SCS M&S Magazine, an invitation for the final phases of its preparation was published (Ören and Waite, 2010). WHAT IS DONE In this article, about 100 definitions of simulation are compiled from seven types of sources as outlined in Table 1. Table 2 shows the three groups and nine types used to categorize the definitions. Table 3 contains all the quoted definitions listed by type of resources and classified in three groups and further in three types within each of the three groups. An early compilation of 22 definitions of simulation spanning from 1961 to 1979 was prepared by Pritsker (1979). An interesting linguistic analysis of "simulation" which gives hyponyms (more specific meanings), synonyms, and hypernyms (more general meanings) of simulation can be found at (WordNet 3.0). Table 1. Categories and types of resources used in collecting the definitions of simulation Early resources • 1960s and 1970s 13 Defense-related resources • Defense-related M&S dictionaries 9 Civilian resources • Civilian M&S dictionaries 3 • Computer dictionaries 5 • Other professional dictionaries (by disciplines) 22 • General-purpose dictionaries and encyclopedias 35 • Scientists and practitioners 10 Table 2. Three groups and nine types used to categorize the definitions group A B C experiment training (experience) game (experience) modeling model implementation / execution technique similarity / imitation pretense / fake other type a1 a2 a3 b1 b2 b3 c1 c2 c3 # entries 24 9 1 12 14 8 19 14 7 PLANS FOR THE FUTURE A companion article will be published in the July issue of the SCS M&S Magazine (Ören 2011b) to attest the richness of M&S discipline where (1) definitions of simulation will be revisited within a unifying framework documented previously (Ören 2009b, 2010, 2011a) and referring to the nine types identified in Table 2, and (2) a list of over 400 terms representing types of simulation will be given. An ontology-based dictionary for the types of simulation is aimed to be developed later (1) to give their definitions, (2) to identify synonyms, and (3) to list them not only in alphabetical order but also in logical groupings which is the essence of ontology-based dictionaries (Ören, Ghasem-Aghaee, and Yilmaz, 2007). Simulationists are kindly invited to share their views on any step of this on-going effort of the preparation of a Body of Knowledge index for modeling and simulation (M&S BoK) by sending their views to the Letters-to-Editor section of the SCS M&S Magazine.