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4+1

4+1 is a view model designed by Philippe Kruchten for describing the architecture of software-intensive systems, based on the use of multiple, concurrent views. The views are used to describe the system in the viewpoint of different stakeholders, such as end-users, developers and project managers. The four views of the model are logical, development, process and physical view. In addition selected use cases or scenarios are utilized to illustrate the architecture. Hence the model contains 4+1 views.

The views

Below each view of the model is described.

Logical view

The logical view is concerned with the functionality that the system provides to end-users.

Development view

The development view illustrates a system from a programmers perspective and is concerned with software management.

Process view

The process view addresses:

• Concurrency
• Distribution
• Integrators
• Performance
• Scalability, etc.

Physical view

The physical view depicts the system from a system engineer's point-of-view. It is concerned with the topology of software components on the physical layer, as well as communication between these components.

Scenarios

The description of an architecture is illustrated using a small set of use cases, or scenarios which become a fifth view. The scenarios describe sequences of interactions between objects, and between processes. They are used to identify architectural elements and to illustrate and validate the architecture design. They also serve as a starting point for tests of an architecture prototype.

References

• Kruchten, Philippe (1995, November). Architectural Blueprints — The “4+1” View Model of Software Architecture. IEEE Software 12 (6), pp. 42-50.