APE Product Tree (mbse.gfse.de)

Could you easily answer this question? Is a document a model? Why not?

Most references define a model or properties of a model like this

A model is a representation of something. It captures not all attributes of the represented thing, but rather only those seeming relevant. The model is created for a certain purpose and stakeholders.

That definition includes text documents. They are also a representation of something and do not capture all attributes of the real thing. However I don’t feel comfortable to call a document a model. If a document is a kind of a model why everybody talks about the shift from document-based to model-based systems engineering.

We must specialize the common definition of a model for systems engineering. I define two additional rules for the MBSE model definition.

The first rule clarifies a typical misunderstanding. MBSE is not only about SysML. MBSE is also about methodologies. And looking on the model you can use many different models and model languages in a MBSE environment. Although SysML is the most important modeling language for MBSE.

The first specific rule for the MBSE model definition is:

[MODEL1] A model could consist of many model repositories.

I separate the terms model and model repository. For example a MBSE model could consist of a requirements model repository (e.g. IBM Rational Doors™) and a SysML model. From the users perspective it is one model. It doesn’t matter that the model data is located in different repositories. You need tool chains to link several model repositories, i.e. bridges, adapters, or a model bus.

The first rule still does not exclude documents from the model definition. A model is build with a model language. Typically the users focus is on the diagram and notation – the so called concrete syntax. Much more important is the world behind the concrete syntax. There is the abstract syntax and semantic of the model elements. Simply spoken the data structure and the meaning. The abstract syntax is the enabler to do computer-based analysis, simulation, traceability and so on. That’s the difference between a model and a drawing.

The second specific rule for the MBSE model definition is:

[MODEL2] A model is build with a model language with an abstract syntax that covers the basic concepts of MBSE like requirements, structural system elements and functions.

SysML is such a modeling language. It has elements like requirements, blocks, activities, and so on. The language “knows” MBSE concepts. A typical text document does not fit to this rule. Even if it has a abstract syntax, the syntax does not cover MBSE concepts. Of course it is possible to specify a textual language with an abstract syntax for MBSE concepts. In that case a text document written with “textual SysML” is a model.

The two rules [MODEL1] and [MODEL2] in addition to the common definition of a model are in summary the

Definition of a MBSE model

A model is a representation of something. It captures not all attributes of the represented thing, but rather only those seeming relevant. The model is created for a certain purpose and stakeholders.

[MODEL1] A model could consist of many model repositories.

[MODEL2] A model is build with a model language with an abstract syntax that covers the basic concepts of MBSE like requirements, structural system elements and functions.

I could think of more aspects like graphical representations, view concepts, simulation, and so on. However they are all optional and not mandatory.

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