The 4 + 1 View Model is a predefined set of views for organizing the design and architecture of a system.  It was developed in 1995 by Philippe Kruchten, formerly the Director of Process Development at Rational Software.

The 4 + 1 View Model gets its name from the 4 primary views and 1 supporting view that are used to capture and communicate different aspects of the system.

The 4 primary views are:

• Logical View:   this view describes the functionality of the system in terms of its static structure and dynamic behavior.
  
• Development View:  this view describes the system from a programmer’s perspective and is concerned with the organization of physical code, its main modules, and their dependencies.
  
• Process View:  this view focuses on the runtime behavior of the system and the elements of the system that relate to process performance.  It includes aspects important to scalability, throughput, and process response times to name a few.
  
• Physical View:  this view shows the system from a system engineer's point-of-view. It is concerned with the deployment of software components across the physical architecture including computers and devices , as well as communication between these components.

The 1 supporting view is:

• Use Case View:  this view describes the functionality of the system from the perspective of external actors.