Copia De: The “4+1” View Model Of Software Architecture

Paper published in IEEE Software 12 (6)
November 1995, pp. 42-50

Architectural Blueprints—The “4+1” View
Model of Software Architecture
Philippe Kruchten
Rational Software Corp.

Abstract
This article presents a model for describing the architecture of software-intensive systems, based on the use
of multiple, concurrent views. This use of multiple views allows to address separately theconcerns of the
various ‘stakeholders’ of the architecture: end-user, developers, systems engineers, project managers, etc.,
and to handle separately the functional and non functional requirements. Each of the five views is described,
together with a notation to capture it. The views are designed using an architecture-centered, scenariodriven, iterative development process.
Keywords: softwarearchitecture, view, object-oriented design, software development process

Introduction
We all have seen many books and articles where one diagram attempts to capture the gist of the architecture
of a system. But looking carefully at the set of boxes and arrows shown on these diagrams, it becomes clear
that their authors have struggled hard to represent more on one blueprint than it canactually express. Are
the boxes representing running programs? Or chunks of source code? Or physical computers? Or merely
logical groupings of functionality? Are the arrows representing compilation dependencies? Or control
flows? Or data flows? Usually it is a bit of everything. Does an architecture need a single architectural
style? Sometimes the architecture of the software suffers scars from asystem design that went too far into
prematurely partitioning the software, or from an over-emphasis on one aspect of software development:
data engineering, or run-time efficiency, or development strategy and team organization. Often also the
architecture does not address the concerns of all its “customers” (or “stakeholders” as they are called at
USC). This problem has been noted by severalauthors: Garlan & Shaw1, Abowd & Allen at CMU,
Clements at the SEI. As a remedy, we propose to organize the description of a software architecture using
several concurrent views, each one addressing one specific set of concerns.

An Architectural Model
Software architecture deals with the design and implementation of the high-level structure of the software. It
is the result of assembling acertain number of architectural elements in some well-chosen forms to satisfy
the major functionality and performance requirements of the system, as well as some other, non-functional
requirements such as reliability, scalability, portability, and availability. Perry and Wolfe put it very nicely
in this formula2, modified by Boehm:
Software architecture = {Elements, Forms,Rationale/Constraints}
Software architecture deals with abstraction, with decomposition and composition, with style and esthetics.
To describe a software architecture, we use a model composed of multiple views or perspectives. In order to
eventually address large and challenging architectures, the model we propose is made up of five main views
(cf. fig. 1):
• The logical view, which is the object model of thedesign (when an object-oriented design method is
used),
• the process view, which captures the concurrency and synchronization aspects of the design,
• the physical view, which describes the mapping(s) of the software onto the hardware and reflects its
distributed aspect,

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the development view, which describes the static organization of the software in its development
environment.

Thedescription of an architecture—the decisions made—can be organized around these four views, and
then illustrated by a few selected use cases, or scenarios which become a fifth view. The architecture is in
fact partially evolved from these scenarios as we will see later.
End-user
Functionality

Programmers
Software management

Development
View

Logical View

Scenarios
Process View...