person Author: Process Fellows
In model-based development, it's essential to distinguish between the concepts of "model", "view", and "diagram", as each serves a specific purpose.

A "model" is an abstraction of reality. It represents the complete system description, but only in terms of the essential elements that are relevant to the modeling context. Irrelevant details are deliberately excluded to maintain clarity and focus. The model is considered "complete" not because it includes every possible detail, but because it captures all significant influencing factors necessary for understanding and analysis within its intended scope. Remark: This definition is applicable as well for the various disciplines, e.g. in case a model is used to define a software architecture. If needed, different modelling techniques (e.g. SysML versus UML) might be used for different disciplines.

A "view" focuses on a particular aspect of the model, such as its structure or behavior. Views are tailored to the needs of specific stakeholders, which means that certain details may be intentionally omitted. However, a view never contains more information than the model itself—it is always a subset or projection of the model. The model remains the authoritative source of truth, while views help stakeholders concentrate on what matters most to them.

A "diagram" is a visual representation of a model with respect to a specific view. It helps communicate the model’s content in a clear and accessible way. Multiple types of diagrams can be used to illustrate different views, depending on the aspect being analyzed and the audience’s needs.