Summary of wikipedia
4+1 is a view model for “describing the architecture of software-intensive systems, based on the use of multiple, concurrent views”. The views describe the system from the viewpoints of different stakeholders: end-users, developers, project managers.
development (implementation) view: illustrates a system from a programmer’s perspective, concerned with software management. UML component diagram.
logical view: functionality provided for end-users. UML class and state diagrams.
physical (deployment) view: depicts system from a system engineer’s POV. Topology of software components on the physical layer and physical connections between them. UML deployment diagram.
process view: dynamic aspects of the system. Processes and communcation, runtime behaviour of the system. Addresses concurrency, distribution, integrators, performance, scalability, etc. UML activity diagram.
scenarios (use case view) (the +1 view): architecture illustrated using a small set of use cases. They describe sequences of interactions between objects and proceses. Serve as starting point for tests of prototype.