“As is used in connection with systems engineering, a model is a qualitative or quantitative representation of a process or endeavor that shows the effects of those factors which are significant for the purposes being considered. Modeling is the process of making a model. Although the model may not represent the actual phenomenon in all respects, it does describe the essential inputs, outputs, and internal characteristics, as well as provide an indication of environmental conditions similar to those of actual equipment.”

—  Harold Chestnut

Source: Systems Engineering Tools, (1965), p. 108; As cited in: Alberto Ortiz (1992, p. 13)

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Harold Chestnut 27
American engineer 1917–2001

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“A model is a qualitative or quantitative representation of a process or endeavor that shows the effects of those factors which are significant for the purposes being considered. A model may be pictorial, descriptive, qualitative, or generally approximate in nature; or it may be mathematical and quantitative in nature and reasonably precise. It is important that effective means for modeling be understood such as analog, stochastic, procedural, scheduling, flow chart, schematic, and block diagrams.”

Harold Chestnut (1917–2001) American engineer

Source: Systems Engineering Tools, (1965), p. 108; As cited in: Alberto Ortiz (1992) Systems engineering concept demonstration, process model http://www.dtic.mil/dtic/tr/fulltext/u2/a265469.pdf. p. 12

“Simulation is the use of models and/or the actual conditions of either the thing being modeled or the environment in which it operates, with the models or conditions in physical, mathematical, or some other form. The purpose of simulation is to explore the various results which might be obtained from the real system by subjecting the model to representative environments which are equivalent to, or in some way representative of, the situations it is desired to understand or investigate. Simulation may involve system hardware and the actual physical environment, or it may involve mathematical models subjected to mathematical forcing or disturbance functions representative of the systems conditions to be studied.”

Harold Chestnut (1917–2001) American engineer

Source: Systems Engineering Tools, (1965), p. 111 as cited in

James Martin (author) photo

“Information engineering has been defined with the reference to automated techniques as follows: An interlocking set of automated techniques in which enterprise models, data models and process models are built up in a comprehensive knowledge-base and are used to create and maintain data-processing systems.”

James Martin (author) (1933–2013) British information technology consultant and writer

Source: Information Engineering (1989), p. viii

August-Wilhelm Scheer photo

“Reference models can be quite comprehensive, consisting of hundreds or thousands of model objects. This is why various levels of aggregation are used. Reference models provide enterprises with an initial process engineering solution, letting them determine the degree of detail of the model and the business content.”

August-Wilhelm Scheer (1941) German business theorist

Source: ARIS architecture and reference models for business process management (2000), p. 380.

“Models are used essentially for evaluation and prediction purposes as well as for the analysis and study of the different parts of the system so that the systems engineer or designer may arrive at sound engineering decisions regarding the system design.”

Harold Chestnut (1917–2001) American engineer

Source: Systems Engineering Tools, (1965), p. 113; As cited in: Alberto Ortiz (1992, p. 12-13)

“In all engineering disciplines nowadays, software engineering excluded, there exists an established engineering process to develop a system, which is accompanied by a number of suited modeling description techniques. Software engineering, being a rather new field, has not as yet established any clear methodical guidance or a fully standardized modeling notation.”

Bernhard Rumpe (1967) German computer scientist

Source: Executable Modeling with UML. A vision or a Nightmare (2002), p. 697

“Enterprise architecture (EA) promotes the belief that an enterprise, as a complex system, can be designed or improved in an orderly fashion achieving better overall results than ad-hoc organisation and design. EA is a co-operative effort of designers, analysts and managers and uses enterprise models in the process… enterprise models carry meaning. This resulted in requirements for the enterprise engineering process, which—if not met—can limit the viability of the process. The analysis of the same factors resulted in requirements for improved Enterprise Modelling Tools.”

Peter Bernus (1949) Hungarian-Australian computer scientist

Peter Bernus (2003) "Enterprise models for enterprise architecture and ISO9000: 2000." Annual Reviews in Control 27.2 : 211-220.

“A model may be pictorial, descriptive, qualitative, or generally approximate in nature, or it may be mathematical and quantitative in nature and reasonably precise.”

Harold Chestnut (1917–2001) American engineer

Source: Systems Engineering Tools, (1965), p. 108

Russell L. Ackoff photo

“The effectiveness of any model used to describe and understand behavior of a particular system as a whole ultimately depends on the degree to which that model accurately represents that system. Nevertheless, there have been and are situations in which application of deterministic or animate models to social systems have produced useful results for a short period of time. However, in a longer run, such mismatches usually result in less than desirable results because critical aspects of the social systems were omitted in the less complex model that was used.”

Russell L. Ackoff (1919–2009) Scientist

Ackoff (1999, p. 34) cited in: Michael C. Jackson (2000) Systems Approaches to Management. p. 234.
1990s

“The Unified Modeling Language (UML) is a general-purpose visual modeling language that is used to specify, visualize, construct, and document the artifacts of a software system. It captures decisions and understanding about systems that must be constructed. It is used to understand, design, browse, configure, maintain, and control information about such systems. It is intended for use with all development methods, lifecycle stages, application domains, and media. The modeling language is intended to unify past experience about modeling techniques and to incorporate current software best practices into a standard approach. UML includes semantic concepts, notation, and guidelines. It has static, dynamic, environmental, and organizational parts. It is intended to be supported by interactive visual modeling tools that have code generators and report writers. The UML specification does not define a standard process but is intended to be useful with an iterative development process. It is intended to support most existing object-oriented development processes.”

James Rumbaugh (1947) Computer scientist, software engineer

James Rumbaugh, Ivar Jacobson & Grady Booch (1998) The Unified Modeling Language Reference Manual. p. 1

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