The Cambridge Advanced Learner's Dictionary defines a model as
A representation of something, either as a physical object which is usually smaller than the real object, or as a simple description of the object which might be used in calculations.I like the informal definition I heard from Jon Whittle last week: A model is an abstraction of the real thing for a specific purpose. However with this definition even a specification document written in Word will be a model and I don't think that makes sense.
Mellor et al. defines a model (Ludewig defines even more formal criteria):
A model is a coherent set of formal elements describing something (for example, a system, bank, phone, or train) built for some purpose that is amenable to a particular form of analysis, such as...With this definition it is quite easy to exclude a Word document as a model, since it isn't composed of formal elements. It can incorporate diagrams based on a model, e.g. a class diagram from an UML model, but not the model itself.
In addition to this there should be a purpose with the model. John Daniels identifies three different types of models, each with a different purpose:
- Conceptual model
- Specification model
- Implementation model
I had great help from my colleague Niklas Mellegård in his licentiate thesis Method and Tool Support for Automotive Software Engineering, which is defended on Thursday 30 September at 13:00 in room Torg 2, Patricia building, Lindholmen. Discussion leader will be Prof. Martin Törngren, Dept of Machine Design, Royal Institute of Technology.