What is a Model?
A Model is a representation of a particular thing with a particular purpose. A model may be physical or just an idea, but it is always a representation with a purpose.
According to Stachowiak, a model needs to possess three features:
- Mapping feature: A model is based on an original.
- Reduction feature: A model only reflects a (relevant) selection of the original’s properties.
- Pragmatic feature: A model needs to be usable in place of the original with respect to some purpose.
The first two features are covered simultaneously if one speaks of a model as a “projection” as this implies both something that is projected (the original) and that some information is lost during the projection. Of course exactly what information is dropped—by an activity called “abstraction”—and what is retained depends on the ultimate purpose the model is going to be used for.
The third feature can be further elaborated by detailing what the pragmatic use of the model is. According to Steinmuller ¨ (1993): A model is information:
- on something (content, meaning)
- created by someone (sender)
- for somebody (receiver)
- or some purpose (usage context)
A model can come in many shapes, sizes, and styles. It is important to emphasize that a model is not the real world but merely a human construct to help us better understand real-world systems. In general, all models have an information input, an information processor, and an output of expected results.
Various Definitions of a Model
There are many definitions of the word model. The following definitions refer to a model as a representation of selected aspects of a domain of interest to the modeler:
- a physical, mathematical, or otherwise logical representation of a system, entity, phenomenon, or process (DoD 1998);
- a representation of one or more concepts that may be realized in the physical world (Friedenthal, Moore, and Steiner 2009); a simplified representation of a system at some particular point in time or space intended to promote understanding of the real system (Bellinger 2004);
- an abstraction of a system, aimed at understanding, communicating, explaining, or designing aspects of interest of that system (Dori 2002); and
a selective representation of some system whose form and content are chosen based on a specific set of concerns; the model is related to the system by an explicit or implicit mapping (Object Management Group 2010). In the context of systems engineering, a model that represents a system and its environment is of particular importance to the system engineer who must specify, design, analyze, and verify systems, as well as share information with other stakeholders. A variety of system models are used to represent different types of systems for different modeling purposes. Some of the purposes for modeling systems are summarized in the topic Why Model?, and a simple taxonomy of the different types of models is described in the topic Types of Models. The modeling standards topic refers to some of the standard system modeling languages and other modeling standards that support MBSE.
A model can have different forms as indicated in the first definition above, including a physical, mathematical, or logical representation. A physical model can be a mockup that represents an actual system, such as a model airplane. A mathematical model may represent possible flight trajectories in terms of acceleration, speed, position, and orientation. A logical model may represent logical relationships that describe potential causes of airplane failure, such as how an engine failure can result in a loss of power and cause the airplane to lose altitude, or how the parts of the system are interconnected. It is apparent that many different models may be required to represent a system-of-interest (SoI).
Why use a model?
Improvement efforts require a model of how your organization works, which functions they need, and how those functions interact. A model gives you an understanding of organizational elements and assists in discussions of how and what can and should be improved.
A model offers the following benefits:
- Provides a common framework and language to help communicate
- Leverages years of experience
- Helps users consider the large picture while focusing n improvement
- Is often supported by trainers and consultants
- Can help solve disagreements by providing agreed-upon standards